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

Tools/Scripts/webkitpy/common/net/buildbot/chromiumbuildbot_unittest.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
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 # met:
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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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 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.net.buildbot.chromiumbuildbot import ChromiumBuildBot
 
 
 class ChromiumBuilderTest(unittest.TestCase):
     def test_results_url(self):
         builder = ChromiumBuildBot().builder_with_name('WebKit Mac10.8 (dbg)')
         self.assertEqual(builder.results_url(),
                          'https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Mac10_8__dbg_')
 
     def test_accumulated_results_url(self):
         builder = ChromiumBuildBot().builder_with_name('WebKit Mac10.8 (dbg)')
         self.assertEqual(builder.accumulated_results_url(),
                          'https://storage.googleapis.com/chromium-layout-test-archives/WebKit_Mac10_8__dbg_/results/layout-test-results')