We couldn't copy to_unicode, to_bytes, to_str into module_utils because
of licensing. So once created it we had two sets of functions that did
the same things but had different implementations. To remedy that, this
change removes the ansible.utils.unicode versions of those functions.
Replace .iteritems() with six.iteritems() everywhere except in
module_utils (because there's no 'six' on the remote host). And except
in lib/ansible/galaxy/data/metadata_template.j2, because I'm not sure
six is available there.