**Reason**:
SolrStore hasn't been updated since April 2012. It is to be used as a search backend for SemanticMediaWiki but it is only used on three (outdated) wikis. Most probably the authors wikis and they are apparently no more reachable.
[[ https://www.mediawiki.org/wiki/Extension:SolrStore | SolrStore ]]
- [x] Archive documentation on `mediawiki.org` ( https://www.mediawiki.org/wiki/Extension:SolrStore )
- [x] Remove from `mediawiki/extensions` / `mediawiki/skins` ( along with in `.gitmodules`)
- [X] Remove tests in `integration/config` ( `zuul/layout.yaml` )
- [x] Remove from `translatewiki` ( `groups/MediaWiki/mediawiki-extensions.txt` )
- [x] Empty repository and add a OBSOLETE file.
- [x] Archive the extension's diffusion repository: ( https://phabricator.wikimedia.org/diffusion/ESOS/ )
- [x] Mark the repository read-only in Gerrit: ( https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/SolrStore )
- [ ] Delete the GitHub mirror: https://github.com/wikimedia/mediawiki-extensions-SolrStore