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

Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
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 #    * Redistributions in binary form must reproduce the above
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.checkout.baselineoptimizer import BaselineOptimizer
 from webkitpy.common.checkout.scm.scm_mock import MockSCM
 from webkitpy.common.host_mock import MockHost
 from webkitpy.common.net.buildbot.buildbot_mock import MockBuilder
 from webkitpy.common.net.layouttestresults import LayoutTestResults
 from webkitpy.common.system.executive_mock import MockExecutive
 from webkitpy.common.system.executive_mock import MockExecutive2
 from webkitpy.common.system.outputcapture import OutputCapture
 from webkitpy.thirdparty.mock import Mock
@@ skipping 1196 matching lines @@
         oc.capture_output()
         self.command._do_one_rebaseline()
         out, _, _ = oc.restore_output()
 
         self.assertEqual(out, 'MOCK STDOUT\n')
         self.assertEqual(self.tool.executive.calls, [
             ['git', 'pull'],
             ['/mock-checkout/third_party/WebKit/Tools/Scripts/webkit-patch', 'auto-rebaseline', '--verbose'],
         ])
         self.assertEqual(self._logs, ['MOCK STDOUT'])