Remove thirdparty/unittest2 from webkitpy and require python2.7.

Tools/Scripts/webkitpy/common/system/logtesting.py

 # Copyright (C) 2010 Chris Jerdonek (cjerdonek@webkit.org)
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 # 1.  Redistributions of source code must retain the above copyright
 #     notice, this list of conditions and the following disclaimer.
 # 2.  Redistributions in binary form must reproduce the above copyright
 #     notice, this list of conditions and the following disclaimer in the
 #     documentation and/or other materials provided with the distribution.
@@ skipping 14 matching lines @@
 Provides support for unit-testing messages logged using the built-in
 logging module.
 
 Inherit from the LoggingTestCase class for basic testing needs.  For
 more advanced needs (e.g. unit-testing methods that configure logging),
 see the TestLogStream class, and perhaps also the LogTesting class.
 
 """
 
 import logging
-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 
 class TestLogStream(object):
 
     """Represents a file-like object for unit-testing logging.
 
     This is meant for passing to the logging.StreamHandler constructor.
     Log messages captured by instances of this object can be tested
     using self.assertMessages() below.
 
@@ skipping 203 matching lines @@
     # an explanation of why we clear the array of messages after
     # asserting its contents.
     def assertLog(self, messages):
         """Assert the current array of log messages, and clear its contents.
 
         Args:
           messages: A list of log message strings.
 
         """
         self._log.assertMessages(messages)