PrefStats seems to be dead and unused, since:
- its special page isn't available on either enwiki or mediawiki.org
- it isn't listed in the config extension list
- its database tables (or at least the replicas on analytics-store) were last updated in in 2014
- it hasn't had a substantive change since the repo was created in 2010.
If PrefStats is in fact dead, decomissioning steps include:
- Update its mediawiki.org page
- Follow steps on mw:Gerrit/Inactive projects
- Archive the Phabricator project
In addition, if it's safe to delete the data, we should:
- Delete the prefstats table from the database