Kernel-rt in RHEL 8.6 had lifecycle exceptions to meet specific customer needs in OCP 4.12. Those needs have been fulfilled and no additional kernel-rt builds are expected going forward. We should remove kernel-rt from extensions in 4.12 and DTK.Also needs to be removed from ocp-build-data https://github.com/openshift-eng/ocp-build-data/blob/openshift-4.12/group.yml#L77-L80

Note, we should not have to do this again in later versions since the lifecycle of kernel-rt aligns with OCP in those versions.