Remove Python 3.3 trove classifier

Testing was dropped in de233b7.

Python 3.3 is end of life. It is no longer receiving bug fixes,
including for security issues. Python 3.3 went EOL on 2017-09-29. For
additional details on support Python versions, see:

https://devguide.python.org/#status-of-python-branches

For details on the Python 3.3 release schedule, see:

https://www.python.org/dev/peps/pep-0398/

setup.py

@@ -54,7 +54,6 @@ def get_long_description():
         'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.3',
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',