localrepo: convert _updatebranchcache from nodespace to revspace _updatebranchcache used to use revlog.reachable. After the switch to revlog.ancestors, we can now clean it up a bit and switch the algorithm from nodes to revs.

discovery: convert legacy part of checkheads to revs from nodes After a recent switch from revlog.reachable to revlog.ancestors, clean up this old call site, switching it from nodes to revs.