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 It is to be used as a search backend for SemanticMediaWiki but it is only used on three (outdated) wikis.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.
- Archive documentation on mediawiki.org ( https://www.mediawiki.org/wiki/Extension:SolrStore )
- Remove from mediawiki/extensions / mediawiki/skins ( along with in .gitmodules)
- Remove tests in integration/config ( zuul/layout.yaml )
- Remove from translatewiki ( groups/MediaWiki/mediawiki-extensions.txt )
- Empty repository and add a OBSOLETE file.
- Archive the extension's diffusion repository: ( https://phabricator.wikimedia.org/diffusion/ESOS/ )
- 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