Create ChangeOpReferenceRemove class.

This simplifies ChangeOpReference by removing the
remove function and putting it in a seperate class
as suggested on...
https://gerrit.wikimedia.org/r/#/c/106897/3/repo/includes/ChangeOp/ChangeOpReference.php

Tests are also included in this changeset as well
as switching all usage of the old changeop to remove
references to use the new changeop

Change-Id: I79304c6235a28dda13bdfc5ba0a6908eec683cea
Merge "Create ChangeOpReferenceRemove class."