Revert previous checkin and just add a comment about constructor_ob.
Revert previous checkin and just add a comment about constructor_ob.

There's no point to passing it anymore, but there's a test that
expects the call to fail if you pass a non-callable object.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator