Apply FlaggedRevs to metawiki for W0.

* See also I644aecd4a6bb60cbfd371f162147d3cbf1a36ab6.
* During deployment, see wmgUseFlaggedRevs guidance in wmf-config/InitialiseSettings.php

* Extra Deployment Info:
http://git.wikimedia.org/blob/operations%2Fmediawiki-config.git/a8723d447344c57a4f40b52eae076c683201a11a/wmf-config%2FInitialiseSettings.php#L10138

Change-Id: I8ef47429f38d0afe3287ec5b1a9bdd19ef4aec2d