Import unittest.mock directly.

We don't need to support Python2 anymore.

Signed-off-by: Bastian Venthur <[email protected]>

tests/__init__.py

@@ -1,6 +1,2 @@
 import unittest  # NOQA
-
-try:
-    from unittest import mock
-except ImportError:
-    import mock  # NOQA
+from unittest import mock  # NOQA