Drop deprecated 'setup.py test' support

Since setuptools v41.5.0 (27 Oct 2019), the 'test' command is formally
deprecated and should not be used. Contributors should run test tests
using tox, pytest, run_test.sh or some other entry point.

For details on the setuptools change, see:

https://setuptools.readthedocs.io/en/latest/history.html#v41-5-0

setup.cfg

@@ -1,6 +1,3 @@
-[aliases]
-test=pytest
-
 [flake8]
 exclude =
     .git/,

setup.py

@@ -3,20 +3,10 @@
 import io
 import os
 import re
-import sys
 
 from setuptools import setup, find_packages
 
 
-setup_requires = []
-if 'test' in sys.argv:
-    # Only add pytest-runner to setup_requires if running tests
-    setup_requires.append('pytest-runner>=2.0,<3dev')
-
-tests_require = [
-    'pytest>=3.0.0',
-]
-
 install_requires = [
     'six>=1.9.0',
     # html5lib requirements
@@ -56,8 +46,6 @@ def get_version():
     zip_safe=False,
     python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*',
     install_requires=install_requires,
-    setup_requires=setup_requires,
-    tests_require=tests_require,
     classifiers=[
         'Development Status :: 5 - Production/Stable',
         'Environment :: Web Environment',