remove amd-sev feature flag from secure boot builds (rh only)

Merge Request Required Information

Summary of Changes

Using the SMM-enabled builds with SEV and secure boot enabled appears to not work. It probably never did, so this isn't a regression. Given that SEV is obsoleted by SEV-ES and SEV-SNP there isn't much value in debugging and fixing that. Just remove the feature flag from the firmware description files instead, so libvirt will not create such configurations.

Approved Bugzilla Ticket

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2169247