ancestor: drop an unused local variable assignment

Caught by PyCharm.

Differential Revision: https://phab.mercurial-scm.org/D7736

mercurial/ancestor.py

@@ -331,7 +331,7 b' class lazyancestors(object):'
 
         Result does not include the null revision."""
         self._parentrevs = pfunc
-        self._initrevs = revs = [r for r in revs if r >= stoprev]
+        self._initrevs = [r for r in revs if r >= stoprev]
         self._stoprev = stoprev
         self._inclusive = inclusive