setup.py is no longer maintained by the global sync. Also the note
in requirements.txt does not apply since pip 20.3. This also removes
workaround for old python which we no longer support.
[1] https://lists.openstack.org/pipermail/openstack-discuss/2023-June/034073.html
Change-Id: If0ea61f0b13f2a76720f30236aae57045cfc48a6