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

Tools/Scripts/webkitpy/layout_tests/models/test_results_unittest.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.layout_tests.models.test_results import TestResult
 
 
 class TestResultsTest(unittest.TestCase):
     def test_defaults(self):
         result = TestResult("foo")
         self.assertEqual(result.test_name, 'foo')
         self.assertEqual(result.failures, [])
         self.assertEqual(result.test_run_time, 0)
 
     def test_loads(self):
         result = TestResult(test_name='foo',
                             failures=[],
                             test_run_time=1.1)
         s = result.dumps()
         new_result = TestResult.loads(s)
         self.assertIsInstance(new_result, TestResult)
 
         self.assertEqual(new_result, result)
 
         # Also check that != is implemented.
         self.assertFalse(new_result != result)