Force setup.py to use distutils

Bug: https://bugs.gentoo.org/563534

--- a/setup.py
+++ b/setup.py
@@ -15,7 +15,7 @@
 from __future__ import absolute_import, division, print_function
 
 import os
-import setuptools
+from distutils.core import setup
 
 
 base_dir = os.path.dirname(__file__)
@@ -31,7 +31,7 @@ with open(os.path.join(base_dir, "CHANGELOG.rst")) as f:
     long_description = "\n".join([long_description, f.read()])
 
 
-setuptools.setup(
+setup(
     name=about["__title__"],
     version=about["__version__"],