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

Tools/Scripts/webkitpy/common/net/unittestresults_unittest.py

 # Copyright (c) 2012, Google Inc. All rights reserved.
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from unittestresults import UnitTestResults
 
 
 class UnitTestResultsTest(unittest.TestCase):
 
     def test_nostring(self):
         self.assertIsNone(UnitTestResults.results_from_string(None))
 
     def test_emptystring(self):
@@ skipping 45 matching lines @@
 Expected: 2.71]]></failure>
       <failure message="Value of: tau&#x0A;  Actual: 6&#x0A;Expected: 6.28" type=""><![CDATA[../../Source/WebKit/chromium/tests/ClassTwoTest.cpp:55
 Value of: tau
   Actual: 6
 Expected: 6.28]]></failure>
     </testcase>
   </testsuite>
 </testsuites>"""
         expected = ["ClassOne.TestOne", "ClassTwo.TestTwo"]
         self.assertEqual(expected, UnitTestResults.results_from_string(multiple_failures_per_test_xml))