Fix tox4 and setuptools errors

- Remove skipsdist that it was never supported and causes breakage
when used with usedevelop.
- disable setuptools autodiscovery

Change-Id: I3dd1ab78de71a2a2feb9e7d59612b5c2a09e1f4a

setup.py

@@ -17,4 +17,5 @@ import setuptools
 
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
+    py_modules=[],
     pbr=True)

tox.ini

@@ -1,7 +1,6 @@
 [tox]
 minversion = 3.18.0
 envlist = pep8
-skipsdist = True
 ignore_basepython_conflict = true
 
 [testenv]