Remove some notes no longer valid

setup.py is no longer maintained by the global sync.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
2 files changed