[tox] Remove now unused types-setuptools dependency (#53)

Since we moved away from setuptools, we don't need to install
that dependency anymore when running mypy.

Author: ldionne

tox.ini

@@ -19,7 +19,6 @@ skip_install = true
 deps =
     mypy >= 0.910
     sqlalchemy-stubs
-    types-setuptools
     types-PyYAML
     types-certifi