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 is 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: I60ab96b2f69748e9fad65a73f168b414c14a857a
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

tox.ini

@@ -24,7 +24,6 @@ deps = -r{toxinidir}/doc/requirements.txt
        -r{toxinidir}/test-requirements.txt
        -r{toxinidir}/requirements.txt
 commands = flake8
-           python setup.py check --restructuredtext --strict
 
 [testenv:genconfig]
 basepython = python3