Unnecessary unittest2 requirement

[adamn]

In the tests, unittest2 is imported.

unittest2 shouldn't be a required package since users of python 2.7 don't need it. Typical methods of importing unittest2 include:

try:
    # check the system path first
    from unittest2 import *
except ImportError:
    if sys.version_info >= (2,7):
        # unittest2 features are native in Python 2.7
        from unittest import *

or

try:
    import unittest
    unittest.skip
except AttributeError:
    import unittest2 as unittest