fix: drop six dependency (#1452)

Fixes #1446 🦕
diff --git a/tests/test__helpers.py b/tests/test__helpers.py
index 90c75ef..ab0bd4b 100644
--- a/tests/test__helpers.py
+++ b/tests/test__helpers.py
@@ -15,12 +15,9 @@
 """Unit tests for googleapiclient._helpers."""
 
 import unittest
+import urllib
 
 import mock
-
-import six
-from six.moves import urllib
-
 from googleapiclient import _helpers