histedit: simplify desthistedit

Instead of sorting the revset and take the first one, take the minimum
revision.

Differential Revision: https://phab.mercurial-scm.org/D3137

mercurial/destutil.py

@@ -350,10 +350,8 b' def desthistedit(ui, repo):'
         revs = scmutil.revrange(repo, [default])
 
     if revs:
-        # The revset supplied by the user may not be in ascending order nor
-        # take the first revision. So do this manually.
-        revs.sort()
-        return revs.first()
+        # Take the first revision of the revset as the root
+        return revs.min()
 
     return None