rebase: remove revprecursor and revpruned states (BC) Those states are no longer necessary for rebase to function properly. Remove them to make the code cleaner. Marked as BC because in a corner case where working parent is obsoleted, and is skipped for rebase, we no longer move working parent after rebase completes. That is better since if working parent is obsoleted, it should be the user moving working parent back there (after a rebase) explicitly, in that case, we shouldn't move working parent again. Differential Revision: https://phab.mercurial-scm.org/D24