Remove setup.py check from pep8 job

Using "python setup.py check -r -s" method of checking the package has
been deprecated with the new recommendation to build the sdist and
wheel, then running "twine check" against the output.

Luckily, there is already a job that covers this that only runs when the
README, setup.py, or setup.cfg files change, making running this in the
pep8 job redundant. This covered by the test-release-openstack-python3
that is defined in the publish-to-pypi-python3 template.

More details can be found in this mailing list post:

http://lists.openstack.org/pipermail/openstack-dev/2018-October/136136.html

Change-Id: I9c760887d90869a44af62f4a4c4c09d3599f6047
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

tox.ini

@@ -45,7 +45,6 @@ deps =
     readme
 commands =
     doc8 doc/source
-    python setup.py check -r -s
     flake8
 
 [testenv:venv]