Hello Guix!

This is my 2nd and hopefully correct attempt at updating python-pip to
9.0.1. Test inputs were removed as the tarball available from pypi is
stripped from any test.

It also incorporates suggestions that were previously made [1]; for
example we no longer need to use setuptools as an input since our Python
package definitions were recently updated to always be built with
pip/setuptools (the ensurepip flag).