MNT: Clean-up setup.cfg
MNT: Clean-up setup.cfg

We removed all linting from the test install, so need to remove
pytest-flake8. Also remove the totally useless and unused [dev] install
target.

dopplershift/MetPy,dopplershift/MetPy,Unidata/MetPy,ShawnMurd/MetPy,Unidata/MetPy