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

Tools/Scripts/webkitpy/common/webkitunittest.py

 # Copyright (C) 2011 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 11 matching lines @@
 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 '''Basic unit test functionality.'''
 
 import re
-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 
 class TestCase(unittest.TestCase):
     def setUp(self):
         # For versions of Python before 2.7.
         if not 'assertRaisesRegexp' in dir(self):
             self.assertRaisesRegexp = self._assertRaisesRegexp
 
     def _assertRaisesRegexp(self, expected_exception, regex_message, callable, *args):
         try:
             callable(*args)
             self.assertTrue(False, 'No assert raised.')
         except Exception, exception:
             self.assertTrue(issubclass(exception.__class__, expected_exception),
                             'Exception type was unexpected.')
             self.assertTrue(re.match(regex_message, exception.__str__()),
                             'Expected regex "%s"\nGot "%s"' % (regex_message, exception.__str__()))