RHEL 8.4 goes of out of Extended Update Support (EUS) by May 31, 2023. With that we'll stop supporting conversions to it.

Acceptance criteria:

• 8.4 is removed from the list of supported EUS releases: https://github.com/oamg/convert2rhel/blob/v1.1/convert2rhel/systeminfo.py#L59
• The hardcoded CentOS 8.4 repos are removed as there's no more use for them
  • https://github.com/oamg/convert2rhel/tree/v1.1/convert2rhel/data/8/x86_64/repos/centos-8.4
• Integration tests are updated to not count with conversions to RHEL 8.4
• The RHEL 8.4 EUS repos can be removed from the Dogfood Satellite server
  • https://gitlab.cee.redhat.com/satellite/satellite-ansible-setup/-/merge_requests/15