Disable counters (wgDisableCounters)

They should not be enabled in production wikis that use page caching
(such as the WMF cluster), since the count will not include cache hits.
Thus, this makes the MWV setup slightly closer to production.

Also, the actual counter is not useful for development work.

Change-Id: I5888fbf291fe4b7608b6c7ed72bf118f36744601