**Reason**:
labs/tools/gerrit-to-redis has been emptied: https://gerrit.wikimedia.org/r/#/c/labs/tools/gerrit-to-redis/+/445556/
People should instead use gerrit stream-events.
- [ ] ~~Archive documentation on `mediawiki.org` (provide URL to the extension/skin here).~~
- [ ] ~~Remove tests in `integration/config` (`zuul/layout.yaml`).~~
- [ ] ~~Remove from `translatewiki` (`groups/MediaWiki/mediawiki-extensions.txt` / `groups/MediaWiki/mediawiki-skins.txt`).~~
- [ ] ~~Remove manifest/other references from `mediawiki/vagrant` if they exist.~~
- [X] Empty repository and add an ARCHIVED file.
- [ ] ~~Remove from https://doc.wikimedia.org/cover-extensions/ if present (requires #continuous-integration-infrastructure shell user to delete directly from the server)~~
- [ ] ~~Archive Phabricator project `<#ProjectX>` for associated extension/skin.~~
- [ ] ~~Edit Phabricator project `<#ProjectX>` description for associated extension/skin with a link to this ticket.~~
- [ ] Archive the extension's diffusion repository: rTGTR
- [X] Mark the repository read-only in Gerrit: https://gerrit.wikimedia.org/r/#/admin/projects/labs/tools/gerrit-to-redis
- [X] Delete the GitHub mirror: https://github.com/wikimedia/labs-tools-gerrit-to-redis