Clean up the Py2/Py3 boilerplate

src/allmydata/test/cli/test_invite.py

@@ -1,24 +1,12 @@
 """
-Ported to Pythn 3.
+Tests for ``tahoe invite``.
 """
-from __future__ import absolute_import
-from __future__ import division
-from __future__ import print_function
-from __future__ import unicode_literals
-
-from future.utils import PY2
-if PY2:
-    from future.builtins import filter, map, zip, ascii, chr, hex, input, next, oct, open, pow, round, super, bytes, dict, list, object, range, str, max, min  # noqa: F401
 
 import os
 import mock
 import json
 from os.path import join
-
-try:
-    from typing import Optional, Sequence
-except ImportError:
-    pass
+from typing import Optional, Sequence
 
 from twisted.trial import unittest
 from twisted.internet import defer