obsolete: drop usage of changectx in '_computephasedivergentset' Changectx are expensive and not needed there. The use of `repo.set` denote old code that predate the introduction of `repo.revs` that we now use. On my mercurial repository 495 draft: before: 0.010275 second after: 0.008832 second On a mercurial repository with 115973 draft: before: 0.899255 second after: 0.397131 second