[Checkins] [zopefoundation/RestrictedPython] 2437e0: Clean up test infrastructure:

[Michael Howitz]

  Branch: refs/heads/master
  Home:   https://github.com/zopefoundation/RestrictedPython
  Commit: 2437e02d1e0f0bc72b01c04c9a4dd734a21ff551
      https://github.com/zopefoundation/RestrictedPython/commit/2437e02d1e0f0bc72b01c04c9a4dd734a21ff551
  Author: Michael Howitz <mh at gocept.com>
  Date:   2019-05-08 (Wed, 08 May 2019)

  Changed paths:
    M .travis.yml
    M tox.ini

  Log Message:
  -----------
  Clean up test infrastructure:

* Lint only once.
* Remove not used flake8 plug-ins.