python-setuptools: use pypi package

python-setuptools: use pypi package

The releases on Github produces a setuptools version that isn't PEP518
compliant because a .post number is attached to the .egg file
(IE: 40.0.0.post20180820) which can cause a python package using setuptools
to fail if looking for a setuptools version.

Instead, using the official release from pypi is recommended as it does not
produce a  .post version on the egg file.

Another benefit is not having to run bootstrap.py either.

See https://github.com/pypa/setuptools/issues/1462 for more details about
the issue

Signed-off-by: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>