**Reason**
Merged into core. A week after prod is updated, the repo can be emptied out.
**To-do list**
- On-wiki documentation
-- [x] Archive documentation on `mediawiki.org` (provide URL): https://www.mediawiki.org/wiki/Extension:PoolCounter
-- [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
-- ~~Close all Phabricator tasks for the extension/skin ~~
-- ~~Archive Phabricator project for the extension/skin.~~
-- [x] Remove from `translatewiki.net` ([[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-extensions.txt | groups/MediaWiki/mediawiki-extensions.txt ]] / [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/WikimediaTechnicalAgg.yaml | groups/MediaWiki/WikimediaTechnicalAgg.yaml ]]).
- Configuration/tests/integrations/etc.
-- [ ] 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
-- [ ] Empty repository, leaving only the README indicating the repo is archived, and referring to this task by URL.
-- [ ] 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`).
-- [ ] Mark the repository read-only in Gerrit (also edit description to prepend "[ARCHIVED]" and a reference to this task): (provide Gerrit Repository URL).
-- [ ] Archive the Diffusion repository for the extension/skin: (provide the Diffusion repository callsign or URL): https://phabricator.wikimedia.org/diffusion/EPOC/
-- [ ] Archive the GitHub mirror: (provide GitHub repository URL): https://github.com/wikimedia/mediawiki-extensions-PoolCounter/