mediawiki.user: Use mw.log.deprecate to track user() and anonymous()

Follows-up I5970be9e859358 which deprecated these orignally.

Also remove obsolete tests now that they're linked by reference.

Change-Id: I559efa8a61de9f7b600c7b74edd5a56fb0a33b00
Merge "mediawiki.user: Use mw.log.deprecate to track user() and anonymous()"