Thanks @MaxSem
Is https://gerrit.wikimedia.org/r/335830 relevant? Does it need amending/abandoning in favour of something else? I'm not sure what the process for undeploying is.
Who's going to make sure this happens? Do we need approval from anyone else?

Disabling the extension is the first step and is a normal configuration change (in this case there is a global consensus), it can be done in multiple steps beginning from https://gerrit.wikimedia.org/r/335830 . Once the extension is disabled everywhere, we can immediately remove the configuration from mediawiki-config and then the branching tools (the reverse of https://wikitech.wikimedia.org/wiki/Heterogeneous_deployment#Add_new_extensions_to_extension-list etc.).

Change 335830 abandoned by Jdlrobson:
Disable RelatedSites on English, French and Italian Wikivoyages

Reason:
Dont know what's happening here.

https://gerrit.wikimedia.org/r/335830

Change 335830 restored by Jdlrobson:
Disable RelatedSites on English, French and Italian Wikivoyages

https://gerrit.wikimedia.org/r/335830

For the record I'm very happy to disable these extensions (I don't like unmaintained code on our cluster), I just want to make sure if challenged I can point to appropriate discussions. The village pump links are very old and it would be good to summarise the outcomes of those discussions.

In T128326#3349777, Jdlrobson wrote:

Okay, there is still not clarity here (due to the dead links in the description an missing links for other projects).

I fixed the dead links in the task description.

@Jdlrobson added a project: Community-Relations-Support.

As the Community-Relations-Support project was added to this task, I am copying their usual template to ask for clarification:

1. What is the problem?
2. How does success of this task look like? How do we know when we are done?
3. Is there any goal, program, project, team related with this request? Please provide links and use the corresponding Phabricator tags when available.
4. What is your expected timeline from start to end? Is there a hard deadline?

Change 335830 abandoned by Jdlrobson:
Disable RelatedSites on English, French and Italian Wikivoyages

https://gerrit.wikimedia.org/r/335830

Created a new discussion on English Wikivoyage here: https://en.wikivoyage.org/wiki/Wikivoyage:Travellers%27_pub#We_need_to_remove_all_the_RelatedSites_links.

Follow up discussion here: https://en.wikivoyage.org/wiki/Wikivoyage:Travellers%27_pub#Please_help_migrate_related_site_links

Newer data, counting unique pages instead of links:

$ foreachwikiindblist wikivoyage.dblist sql.php --query="select iwl_prefix, count(distinct(iwl_from)) as num from iwlinks where iwl_prefix in ('wikipedia', 'commons', 'dmoz', 'citizendium') group by iwl_prefix order by num desc" | grep '\['
bnwikivoyage:      [iwl_prefix] => commons
bnwikivoyage:      [num] => 3
dewikivoyage:      [iwl_prefix] => commons
dewikivoyage:      [num] => 810
dewikivoyage:      [iwl_prefix] => wikipedia
dewikivoyage:      [num] => 799
dewikivoyage:      [iwl_prefix] => dmoz
dewikivoyage:      [num] => 2
dewikivoyage:      [iwl_prefix] => citizendium
dewikivoyage:      [num] => 1
elwikivoyage:      [iwl_prefix] => commons
elwikivoyage:      [num] => 1032
elwikivoyage:      [iwl_prefix] => wikipedia
elwikivoyage:      [num] => 2
enwikivoyage:      [iwl_prefix] => commons
enwikivoyage:      [num] => 1270
enwikivoyage:      [iwl_prefix] => wikipedia
enwikivoyage:      [num] => 1218
enwikivoyage:      [iwl_prefix] => dmoz
enwikivoyage:      [num] => 7
eswikivoyage:      [iwl_prefix] => commons
eswikivoyage:      [num] => 1093
eswikivoyage:      [iwl_prefix] => wikipedia
eswikivoyage:      [num] => 21
fawikivoyage:      [iwl_prefix] => commons
fawikivoyage:      [num] => 153
fawikivoyage:      [iwl_prefix] => wikipedia
fawikivoyage:      [num] => 16
fiwikivoyage:      [iwl_prefix] => wikipedia
fiwikivoyage:      [num] => 134
fiwikivoyage:      [iwl_prefix] => commons
fiwikivoyage:      [num] => 4
frwikivoyage:      [iwl_prefix] => wikipedia
frwikivoyage:      [num] => 243
frwikivoyage:      [iwl_prefix] => commons
frwikivoyage:      [num] => 151
hewikivoyage:      [iwl_prefix] => commons
hewikivoyage:      [num] => 1771
hewikivoyage:      [iwl_prefix] => wikipedia
hewikivoyage:      [num] => 7
hiwikivoyage:      [iwl_prefix] => commons
hiwikivoyage:      [num] => 3
itwikivoyage:      [iwl_prefix] => commons
itwikivoyage:      [num] => 88
itwikivoyage:      [iwl_prefix] => wikipedia
itwikivoyage:      [num] => 23
nlwikivoyage:      [iwl_prefix] => wikipedia
nlwikivoyage:      [num] => 157
nlwikivoyage:      [iwl_prefix] => commons
nlwikivoyage:      [num] => 28
nlwikivoyage:      [iwl_prefix] => dmoz
nlwikivoyage:      [num] => 1
plwikivoyage:      [iwl_prefix] => wikipedia
plwikivoyage:      [num] => 30
plwikivoyage:      [iwl_prefix] => commons
plwikivoyage:      [num] => 22
pswikivoyage:      [iwl_prefix] => commons
pswikivoyage:      [num] => 3
ptwikivoyage:      [iwl_prefix] => wikipedia
ptwikivoyage:      [num] => 114
ptwikivoyage:      [iwl_prefix] => commons
ptwikivoyage:      [num] => 27
ptwikivoyage:      [iwl_prefix] => dmoz
ptwikivoyage:      [num] => 1
rowikivoyage:      [iwl_prefix] => commons
rowikivoyage:      [num] => 14
rowikivoyage:      [iwl_prefix] => wikipedia
rowikivoyage:      [num] => 3
ruwikivoyage:      [iwl_prefix] => commons
ruwikivoyage:      [num] => 3106
ruwikivoyage:      [iwl_prefix] => wikipedia
ruwikivoyage:      [num] => 210
svwikivoyage:      [iwl_prefix] => commons
svwikivoyage:      [num] => 33
svwikivoyage:      [iwl_prefix] => wikipedia
svwikivoyage:      [num] => 21
ukwikivoyage:      [iwl_prefix] => commons
ukwikivoyage:      [num] => 24
ukwikivoyage:      [iwl_prefix] => wikipedia
ukwikivoyage:      [num] => 13
viwikivoyage:      [iwl_prefix] => wikipedia
viwikivoyage:      [num] => 147
viwikivoyage:      [iwl_prefix] => commons
viwikivoyage:      [num] => 21
zhwikivoyage:      [iwl_prefix] => commons
zhwikivoyage:      [num] => 128
zhwikivoyage:      [iwl_prefix] => wikipedia
zhwikivoyage:      [num] => 34
zhwikivoyage:      [iwl_prefix] => dmoz
zhwikivoyage:      [num] => 1

How fresh is the iwlinks table? EN Wikivoyage manually replaced all known links, but this shows 1218 pages still link to Wikipedia.

Here's an explanation for what's going on:

Number of pages using RelatedSites on given wikivoyage:

bnwikivoyage:      [num] => 3
dewikivoyage:      [num] => 1593
elwikivoyage:      [num] => 1034
enwikivoyage:      [num] => 2376
eswikivoyage:      [num] => 1110
fawikivoyage:      [num] => 169
fiwikivoyage:      [num] => 138
frwikivoyage:      [num] => 375
hewikivoyage:      [num] => 1777
hiwikivoyage:      [num] => 3
itwikivoyage:      [num] => 109
nlwikivoyage:      [num] => 183
plwikivoyage:      [num] => 47
pswikivoyage:      [num] => 3
ptwikivoyage:      [num] => 138
rowikivoyage:      [num] => 17
ruwikivoyage:      [num] => 3222
svwikivoyage:      [num] => 53
ukwikivoyage:      [num] => 35
viwikivoyage:      [num] => 168
zhwikivoyage:      [num] => 161

Interesting that bnwikivoyage did not show up in the data from last year but it does now. We could be doing a better job at announcing deprecations. :)

These numbers do not match up with the number of pages in the category Pages using RelatedSites(or equivalent) on these wikis. For example on English wikivoyage there's only 112 pages using RelatedSites according to the category. But the category page does not show all of the pages it should because those pages got the category added automatically and it's not until those pages are edited by someone that they will be "refreshed" and start showing up in the category page, if that makes sense.

So the first thing we need to do is get the categories updated and then move to get consensus for removing RelatedSites from the projects. According to Max, it should not be hard to run a script to do the cleanup instead of having our editors do it.

OK, found the problem: the iwlinks can't be used for what I'm trying to do at all. The only reasonable way is probably something like this search (note the namespaces: only subject and additionally File: is excluded to avoid results from Commons).

In T128326#4303957, @MaxSem wrote:

OK, found the problem: the iwlinks can't be used for what I'm trying to do at all. The only reasonable way is probably something like this search (note the namespaces: only subject and additionally File: is excluded to avoid results from Commons).

So you're saying the category pages are definitely incorrect?

Due to the way tracking categories are populated, I'd rather trust search, unless somebody wants to run refreshLinks.php across all Wikivoyages.

In T128326#4303910, @Niharika wrote:

Interesting that bnwikivoyage did not show up in the data from last year but it does now.

bnwikivoyage did not exist (as a separate wiki) until this month (T196357).

Change 452181 had a related patch set uploaded (by Amire80; owner: Amire80):
[translatewiki@master] Move DisableAccount and RelatedSites to the Legacy group

https://gerrit.wikimedia.org/r/452181

Change 452181 merged by jenkins-bot:
[translatewiki@master] Move DisableAccount and RelatedSites to the Legacy group

https://gerrit.wikimedia.org/r/452181

Just wanted to mention that some questions by the Wikivoyage community pend response here:
https://meta.wikimedia.org/wiki/Talk:Community_Tech/Deprecation_of_RelatedSites_extension
It would be nice if any of the developers enter the discussion. Thank you!

I replied to the inquiry on meta. I think we're good to move ahead.

Change 471886 had a related patch set uploaded (by MaxSem; owner: MaxSem):
[translatewiki@master] Remove RelatedSites from Wikimedia list

https://gerrit.wikimedia.org/r/471886

Change 471886 merged by jenkins-bot:
[translatewiki@master] Remove RelatedSites from Wikimedia list

https://gerrit.wikimedia.org/r/471886