Remove hitcounters and associated code

The hitcounter implementation in MediaWiki is flawed
and needs removal. For proper metrics, it is suggested to use
something like Piwik or Google Analytics.

RFC: https://www.mediawiki.org/wiki/Requests_for_comment/Removing_hit_counters_from_MediaWiki_core
Change-Id: I0e5006a7e8a09c800f8fa4effa9399e8afdd7a57
Merge "Remove hitcounters and associated code"