branchmap: remove redundant sort

There is absoluty no benefit in sorting a list that's being merged into a set
on the next line. The changelog.ancestors() call later on also doesn't benefit
from a sorted sequence of revs.

Differential Revision: https://phab.mercurial-scm.org/D5111

mercurial/branchmap.py

@@ -296,7 +296,6 b' class branchcache(dict):'
             # This have been tested True on all internal usage of this function.
             # run it again in case of doubt
             # assert not (set(bheadrevs) & set(newheadrevs))
-            newheadrevs.sort()
             bheadset.update(newheadrevs)
 
             # This prunes out two kinds of heads - heads that are superseded by