PageArchive::getRevision was deprecated in T194015: Make PageArchive aware of MCR in favor of a new method (the getArchivedRevision, since updated to getArchivedRevisionRecord)
getRevision retrieves the Revision object corresponding to a timestamp. Its replacements retrieve based on revision ids.
How should callers be updated? Specifically, for the method to be hard deprecated, Special:Undelete needs to stop using the method, but I'm unsure how to replace it.