context: simplify workingctx._parents

mercurial/context.py

@@ -885,8 +885,7 b' class workingctx(changectx):'
         p = self._repo.dirstate.parents()
         if p[1] == nullid:
             p = p[:-1]
-        self._parents = [changectx(self._repo, x) for x in p]
-        return self._parents
+        return [changectx(self._repo, x) for x in p]
 
     def status(self, ignored=False, clean=False, unknown=False):
         """Explicit status query