[Distutils] Decommissioning last.pypi.python.org

I am shortly going to delete last.pypi.python.org. We've checked with all versions of pip, this will not cause any user-facing disruptions and --use-mirrors will be converted into a no-op. Individual \w.pypi.python.org domains will remain in accordance with the PEP until they request to be redirected. If you are doing something outside of pip using the autodiscovery protocol, now would be the time to fix it. --Noah