BugWatchUpdater.updateBugWatch() shouldn't take can_foo parameters

At the moment BugWatchUpdater.updateBugWatch() takes parameters for can_import_comments, can_push_comments and can_back link. However, these are already defined as attributes of the class that instantiates BugWatchUpdater, RemoteBugUpdater, and a copy of the instantiating object is passed to the BugWatchUpdater as it's created, so there's really no need for these parameters to be passed.

The parameters should be removed and tests should be updated to use a RemoteBugUpdater object as the parent for new BugWatchUpdaters. (Note, I would do this in my current branch, but it's already too large).