Revert changes to setup.py
07c45043b34d1b967d15490ae072f79772bff767 converts from distutils to
setuptools, but it seems the latest setuptools doesn't read MANIFEST
causing the build to fail (and also is missing a lot of files in
`test/`).
Temporarily revert it. We should probably rewrite to use a declarative
format at some point anyway.
Signed-off-by: Michel Alexandre Salim <salimma@fedoraproject.org>