Reason
Per T344746 the development has been moved to GitHub and will move to Wikimedia GitLab soon.

To-do list

• This task
  • Add maintainers of that extension/skin as subscribers to this task (if they have no apparent Phabricator account, notify them on-wiki or via email if possible and note it here).
  • Add Phabricator project <#ProjectX> as a tag for this task, and remove MediaWiki-extensions-Other/Other-skins as appropriate.
• On-wiki documentation
  • Remove tests in integration/config (zuul/layout.yaml).
  • Empty repository, leaving only the README indicating the repo is archived, and referring to this task by URL.
  • Mark the repository read-only in Gerrit (also edit description to prepend "[ARCHIVED]" and a reference to this task): https://gerrit.wikimedia.org/g/wikidata/propertysuggester/RecommenderServer
  • Deactivate the Diffusion repository for the extension: https://phabricator.wikimedia.org/diffusion/DPRS/
  • Delete the GitHub mirror: https://github.com/wikimedia/wikidata-propertysuggester-RecommenderServer