Clear up duplicate /var/log/mediawiki/wikidata dir

* Consolidate logging dir config in mediawiki::sync ('sync' is possibly
  misnamed, but it is where we're consolidating directory resources).
* Remove duplicate definition of /var/log/mediawiki/wikidata.

Change-Id: I96020da7303b77a5dbea0f6bf99dc5d5779d0300