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

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

 # vim: set fileencoding=utf-8 :
 # Copyright (C) 2010 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #    * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #    * Redistributions in binary form must reproduce the above
@@ skipping 17 matching lines @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 # NOTE: The fileencoding comment on the first line of the file is
 # important; without it, Python will choke while trying to parse the file,
 # since it includes non-ASCII characters.
 
 import os
 import stat
 import sys
 import tempfile
-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.system.filesystem import FileSystem
 
 
 class GenericFileSystemTests(object):
     """Tests that should pass on either a real or mock filesystem."""
     # pylint gets confused about this being a mixin: pylint: disable=E1101
     def setup_generic_test_dir(self):
         fs = self.fs
         self.generic_test_dir = str(self.fs.mkdtemp())
@@ skipping 252 matching lines @@
         fs = FileSystem()
         self.assertTrue(fs.remove('filename', remove_with_exception))
         self.assertEqual(-1, RealFileSystemTest._remove_failures)
 
     def test_sep(self):
         fs = FileSystem()
 
         self.assertEqual(fs.sep, os.sep)
         self.assertEqual(fs.join("foo", "bar"),
                           os.path.join("foo", "bar"))