Fix the compatibility docstring

test/helpers.py

@@ -3,15 +3,8 @@ A helper module for testing, improves compatibility for testing (as
 ``jedi._compatibility``) as well as introducing helper functions.
 """
 
-import sys
 from contextlib import contextmanager
 
-if sys.hexversion < 0x02070000:
-    import unittest2 as unittest
-else:
-    import unittest
-TestCase = unittest.TestCase
-
 import os
 import pytest
 from os.path import abspath, dirname, join