remove python setup.py test

[zzzeek]

references:

sqlalchemy/sqlalchemy#4789

pypa/setuptools#1684

pytest-dev/pytest#5546

[sqla-tester]

Mike Bayer has proposed a fix for this issue in the master branch:

remove python setup.py test https://gerrit.sqlalchemy.org/1437

[zzzeek]

we forgot to remove test_requires

[sqla-tester]

Mike Bayer has proposed a fix for this issue in the master branch:

Remove tests_require https://gerrit.sqlalchemy.org/1475