Remove stale pip-missing-reqs and pypy tox tests
Remove stale pip-missing-reqs and pypy tox tests

pip_missing_reqs tool is no longer maintained and has broken with
release 10 of pip

Refer to:
 http://lists.openstack.org/pipermail/openstack-dev/2018-April/130027.html

Change-Id: I38501c409d46a9ad400d55c51934660992e586d8

openstack/oslo.reports