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

Tools/Scripts/webkitpy/layout_tests/port/linux_unittest.py

 # Copyright (C) 2011 Google Inc. All rights reserved.
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.system import executive_mock
 from webkitpy.common.system.systemhost_mock import MockSystemHost
 from webkitpy.tool.mocktool import MockOptions
 
 from webkitpy.layout_tests.port import linux
 from webkitpy.layout_tests.port import port_testcase
 
 
 class LinuxPortTest(port_testcase.PortTestCase):
@@ skipping 58 matching lines @@
         # Test that optional relative paths are returned unmodified.
         options = MockOptions(configuration='Release', build_directory='foo')
         self.assert_build_path(options, ['/mock-checkout/out/Release'], 'foo/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')