sync-wikiversion: don't overwrite AbstractSync
sync-wikiversions implements AbstractSync, but overwrites the main
method which clobbers much of the logic of AbstractSync. We ran into a
problem when AbstractSync was extended to include logic to sync masters.
Now AbstractSync supports canaries but sync-wikiversions does not.
Rather than add-in canary support for sync-wikiversions, I've opted to
have sync-wikiversions use AbstractSync's main method. This means that
sync-wikiversions will perform sync-masters, canary and proxy fan-out
steps which will make it slower, but hopefully safer.
Reviewers: mmodell, dduvall, bd808, Release-Engineering-Team
Reviewed By: mmodell, Release-Engineering-Team
Differential Revision: https://phabricator.wikimedia.org/D1100