Remove metadata from setup.py

- Remove metadata from setup.py
- Split flake8 section into .flake8 from setup.cfg
- tox: set isolated_build=true

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

setup.py

@@ -1,5 +1,2 @@
-#!/usr/bin/env python
-
-from setuptools import setup
-
-setup(setup_requires=["setuptools_scm"], use_scm_version=True)
+import setuptools
+setuptools.setup()