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

Tools/Scripts/webkitpy/layout_tests/port/mac_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.port import mac
 from webkitpy.layout_tests.port import port_testcase
 from webkitpy.tool.mocktool import MockOptions
 
 
 class MacPortTest(port_testcase.PortTestCase):
     os_name = 'mac'
     os_version = 'snowleopard'
     port_name = 'mac'
@@ skipping 59 matching lines @@
         # Check with 'xcodebuild' being newer.
         port.host.filesystem.mtime = lambda f: 5 if '/xcodebuild/' in f else 4
         self.assertEqual(port._build_path(), '/mock-checkout/xcodebuild/Release')
 
     def test_driver_name_option(self):
         self.assertTrue(self.make_port()._path_to_driver().endswith('Content Shell'))
         self.assertTrue(self.make_port(options=MockOptions(driver_name='OtherDriver'))._path_to_driver().endswith('OtherDriver'))
 
     def test_path_to_image_diff(self):
         self.assertEqual(self.make_port()._path_to_image_diff(), '/mock-checkout/out/Release/image_diff')