remove unittest2 and fix various warnings in py3

pelican/tests/support.py

@@ -9,6 +9,7 @@ import sys
 from six import StringIO
 import logging
 from logging.handlers import BufferingHandler
+import unittest
 
 from functools import wraps
 from contextlib import contextmanager
@@ -18,11 +19,6 @@ from shutil import rmtree
 from pelican.contents import Article
 from pelican.settings import _DEFAULT_CONFIG
 
-try:
-    import unittest2 as unittest
-except ImportError:
-    import unittest
-
 
 @contextmanager
 def temporary_folder():