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

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

 # Copyright (C) 2010 Google Inc. All rights reserved.
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-import webkitpy.thirdparty.unittest2 as unittest
 import sys
+import unittest
 
 from webkitpy.common.system.systemhost import SystemHost
 from webkitpy.common.system.platforminfo import PlatformInfo
 from webkitpy.common.system.platforminfo_mock import MockPlatformInfo
 from webkitpy.common.system import path
 
 class AbspathTest(unittest.TestCase):
     def platforminfo(self):
         return SystemHost().platform
 
@@ skipping 30 matching lines @@
 
         # Call cygpath to ensure the subprocess is running.
         path.cygpath("/cygdrive/c/foo.txt")
         self.assertTrue(path._CygPath._singleton.is_running())
 
         # Stop it.
         path._CygPath.stop_cygpath_subprocess()
 
         # Ensure that it is stopped.
         self.assertFalse(path._CygPath._singleton.is_running())