As far as I can tell, the only use was removed in rMW0344ea9ffff1: * (bug 21279) Special:RevisionDelete now uses revision ID for deleted-page… back in 2011 as part of T23279: Regular deletion of revisions deleted with rev_deleted breaks links in log entries
Suggest removing the method (either with or without a deprecation period)
Codesearch: https://codesearch.wmcloud.org/search/?q=checkRevisionExistence&i=nope&files=&repos=