remotefilelog: rename wireproto methods and remaining capabilities This is a mess, in part because there should be more constants throughout. I know we typically do exp- instead of the x_ business in this change, but I also had to use this in some function names, so I figured until I can break that coupling I'd go with this. If it's too unpleasant during review, let me know and I can probably clean it up some more. # no-check-commit due to new foo_bar naming - too hard to avoid right now :( Differential Revision: https://phab.mercurial-scm.org/D5129