revset.only: use cl.findmissingrevs

ancestor.missingancestors is really an implementation detail.

mercurial/revset.py

@@ -10,7 +10,6 b' import parser, util, error, discovery, h'
 import node
 import heapq
 import match as matchmod
-import ancestor as ancestormod
 from i18n import _
 import encoding
 import obsolete as obsmod
@@ -406,7 +405,7 b' def only(repo, subset, x):'
     else:
         exclude = getset(repo, spanset(repo), args[1])
 
-    results = set(ancestormod.missingancestors(include, exclude, cl.parentrevs))
+    results = set(cl.findmissingrevs(common=exclude, heads=include))
     return subset & results
 
 def bisect(repo, subset, x):