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

Tools/Scripts/webkitpy/layout_tests/controllers/test_result_writer_unittest.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
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 # modification, are permitted provided that the following conditions are
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 #     * Redistributions of source code must retain the above copyright
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 #     * Redistributions in binary form must reproduce the above
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 import optparse
-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.system.systemhost_mock import MockSystemHost
 from webkitpy.layout_tests.controllers.test_result_writer import write_test_result
 from webkitpy.layout_tests.port.driver import DriverOutput
 from webkitpy.layout_tests.port.test import TestPort
 from webkitpy.layout_tests.models import test_failures
 
 
 class TestResultWriterTests(unittest.TestCase):
     def run_test(self, failures=None, files=None):
@@ skipping 27 matching lines @@
     def test_reference_is_missing(self):
         failure = test_failures.FailureReftestMismatch()
         failure.reference_filename = 'notfound.html'
         written_files = self.run_test(failures=[failure], files={})
         self.assertEqual(written_files, {})
 
         failure = test_failures.FailureReftestMismatchDidNotOccur()
         failure.reference_filename = 'notfound.html'
         written_files = self.run_test(failures=[failure], files={})
         self.assertEqual(written_files, {})