unstable: use the `_mutablerevs` function when computing content divergent

This is a useful function to get the revision relevant to these computation,
lets make sure all code use it, so that we can improve that `_mutablerevs`
function in a later changeset.

mercurial/obsolete.py

@@ -1016,7 +1016,8 b' def _computecontentdivergentset(repo):'
     obsstore = repo.obsstore
     newermap = {}
     tonode = repo.changelog.node
-    for rev in repo.revs(b'(not public()) - obsolete()'):
+    candidates = sorted(_mutablerevs(repo) - getrevs(repo, b"obsolete"))
+    for rev in candidates:
         node = tonode(rev)
         mark = obsstore.predecessors.get(node, ())
         toprocess = set(mark)