The MobileDiff page no longer exists, and was replaced with a redirect
that redirects to the desktop diff page, so this code can safely
be removed.
Bug: T360389
Change-Id: I8ebe2bc88a650caf29a5755013e980fe3b5aaeb0
User-options related classes are being moved to
the MediaWiki\User\Options namespace in MediaWiki Core;
reflect that change here.
Bug: T352284
Depends-On: I42653491c19dde5de99e0661770e2c81df5d7e84
Change-Id: I5b9f4c7ea90f492f75b9055b801ec0853da22687
