**Reason**
Abandoned for years, uses legacy Revision objects, and apparently broken in several other ways per posts on the talk page
**To-do list**
- This task
-- [x] Add maintainers of that extension/skin as subscribers to this task (if they have no apparent Phabricator account, notify them on-wiki or via email if possible and note it here).
-- [ ] ~~Add Phabricator project <#ProjectX> as a tag for this task, and remove #mediawiki-extensions-other/#other-skins as appropriate.~~
- On-wiki documentation
-- [x] Archive documentation on `mediawiki.org` (provide URL): replace page contents with `{{Archived extension|last revision id before archiving|task=T######}}` (for extensions)/`{{Archived skin|last revision|task=T######}}` (for skins); replace `T######` with this task's number.
-- [ ] ~~If documentation page was translatable, remove `<translate>`, visit Special:PageTranslation, and click "remove from translation" (if you don't have the translation administrator right, ask a [[ https://www.mediawiki.org/wiki/Special:ListUsers/translationadmin | user who does ]]).~~
-- [x] Update Wikidata item (provide URL) associated with documentation page
--- [x] add statement `Abandonware (Q281039)` to `instance of (P31)` together with qualifier `start time (P580)` = the YYYY-MM-DD date that you decided to archive extension/skin (generally per edit history)
--- [x] add qualifier `end time (P582)` = the YYYY-MM-DD (same date as above) to `instance of (P31) = MediaWiki extension (Q6805426)/MediaWiki skin (Q21996535)`
- Phabricator
-- [x] Mark all Phabricator tasks for the extension/skin either Declined or Invalid. Add a comment pointing to this task when doing so for reference.
-- [ ] ~~Archive Phabricator project <#ProjectX> for the extension/skin.~~
-- [ ] ~~Edit Phabricator project <#ProjectX> description for the extension/skin with a link to this ticket.~~
- Translatewiki.net/translations
-- [x] If the extension is deployed on Wikimedia sites, but it is known that it's not going to receive significant feature updates or deployed to new wikis, make sure that its project ids (usually "ext-//extensionname//") appear in the groups/MediaWiki/WikimediaLegacyAgg.yaml file in the translatewiki Gerrit repository and not in WikimediaMainAgg.yaml, WikimediaAdvancedAgg.yaml, etc. (If it also has an api group, it should remain in WikimediaTechnicalAgg.yaml).
-- [x] If the extension is no longer deployed on Wikimedia sites, remove it from all Wikimedia*Agg.yaml. (If it was ever deployed, by this time, it's most likely in WikimediaLegacyAgg.yaml or WikimediaTechnicalAgg.yaml.)
-- [x] If the extension is going to be completely archived and no longer developed, remove it completely from translatewiki.net by making sure that its project IDs don't appear in any of the following files:
--- [x] [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/ExtensionsAgg.yaml | groups/MediaWiki/ExtensionsAgg.yaml ]]
--- [x] [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/SkinsAgg.yaml | groups/MediaWiki/SkinsAgg.yaml ]]
--- [x] [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-extensions.txt | groups/MediaWiki/mediawiki-extensions.txt ]]
--- [x] [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-skins.txt | groups/MediaWiki/mediawiki-skins.txt ]]
--- [x] [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/repoconfig.yaml | repoconfig.yaml ]]
--- [x] [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/mw-config/validation-exclusion-list.php | mw-config/validation-exclusion-list.php ]]
- Configuration/tests/integrations/etc.
-- [x] Remove tests in [[ https://gerrit.wikimedia.org/g/integration/config | integration/config ]] ([[ https://gerrit.wikimedia.org/r/plugins/gitiles/integration/config/+/master/zuul/layout.yaml | zuul/layout.yaml ]]).
-- [ ] ~~Remove manifest/other references from [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/vagrant/+/master | mediawiki/vagrant ]] if they exist.~~
-- [ ] ~~Remove from https://doc.wikimedia.org/cover-extensions/ if present (requires #continuous-integration-infrastructure shell user to delete directly from the server).~~
- Repositories
-- [x] Empty repository, leaving only the README indicating the repo is archived, and referring to this task by URL.
-- [x] Remove from [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/+/master | mediawiki/extensions ]] / [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/skins/+/master | mediawiki/skins ]] (along with in `.gitmodules`).
-- [x] Mark the repository read-only in Gerrit (also edit description to prepend "[ARCHIVED]" and a reference to this task, remove all access lists and reparent on `All-Archived-Project`): (provide Gerrit Repository URL).
-- [x] Deactivate the Diffusion repository for the extension/skin: https://phabricator.wikimedia.org/diffusion/ECHE/
-- [x] Delete the GitHub mirror: https://github.com/wikimedia/mediawiki-extensions-Checkpoint