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

Tools/Scripts/webkitpy/tool/mocktool_unittest.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from mocktool import MockOptions
 
 
 class MockOptionsTest(unittest.TestCase):
     # MockOptions() should implement the same semantics that
     # optparse.Values does.
 
     def test_get__set(self):
         # Test that we can still set options after we construct the
         # object.
         options = MockOptions()
         options.foo = 'bar'
         self.assertEqual(options.foo, 'bar')
 
     def test_get__unset(self):
         # Test that unset options raise an exception (regular Mock
         # objects return an object and hence are different from
         # optparse.Values()).
         options = MockOptions()
         self.assertRaises(AttributeError, lambda: options.foo)
 
     def test_kwarg__set(self):
         # Test that keyword arguments work in the constructor.
         options = MockOptions(foo='bar')
         self.assertEqual(options.foo, 'bar')