Over the years, [[ https://www.mediawiki.org/wiki/Category:Archived_extensions | more than a thousand extensions ]] have been archived on Mediawiki.org. Doubtless for many of them, this archival was done without concern for other traces related to the extensions; {T190671} and {T201250} are examples of a specific type of leftover and of an incompletely archived extension, respectively; the latter task shows that even extensions or skins which were archived years ago (Extension:LilyPond was archived on Mediawiki.org in 2013) can still have lingering traces. We should track all of these down and clean them up.
Note that this ticket is not specifically about extensions/skins archived on Mediawiki.org, but also about any archived in Gerrit, etc.
For reference, these are the currently known possible leftovers we would care about and could address:
* Documentation on `mediawiki.org`.
* Wikidata items.
* Entries in `mediawiki/extensions`/`mediawiki/skins` (along with in `.gitmodules`).
* Tests in `integration/config` (`zuul/layout.yaml`).
* Messages on `translatewiki.net` (`groups/MediaWiki/mediawiki-extensions.txt`/`groups/MediaWiki/mediawiki-skins.txt`).
* Manifest and other references in `mediawiki/vagrant`.
* Integration stuff on https://doc.wikimedia.org/cover-extensions/ if present (requires #continuous-integration-infrastructure shell user to delete directly from the server)
* Phabricator project or open tasks.
* Diffusion repository.
* Gerrit repository.
* GitHub mirror.