**Reason**: https://www.mediawiki.org/wiki/Extension:Ads (rEADS) is not mantained and looking at its commit history the only regular activity is updating builds and translations that come from translatewiki. Archiving this extension seems a sensible option.
- [x] Archive documentation on `mediawiki.org`.
- [x] Remove from `mediawiki/extensions` (along with in `.gitmodules`).
- [x] Remove tests in `intregation/config` (`zuul/layout.yaml`).
- [x] Remove from `translatewiki` (`groups/MediaWiki/mediawiki-extensions.txt`).
- [x] Empty gerrit repository, add `OBSOLETE` file and merge the changes.
- [ ] Mark the repository read-only in Gerrit.
- [ ] Archive the extension's diffusion repository.
- [ ] Delete GitHub mirror.
* Track gerrit changes: https://gerrit.wikimedia.org/r/#/q/topic:T175495