Drop custom CMake macros, RHEL 8.4 includes them now (cf. rhbz#1858983)
Starting with Red Hat Enterprise Linux 8.4, CMake was rebased to v3.18
and the CMake macros were synced from Fedora to RHEL. This obviates
the need for our version, so let's drop them.
Reference: https://bugzilla.redhat.com/1816874
Reference: https://bugzilla.redhat.com/1858983