Description of problem:
default cpu_mode set as host-passthrough in ComputeResource Libvirt after fix in https://bugzilla.redhat.com/show_bug.cgi?id=2236693

Version-Release number of selected component (if applicable):
Satellite 6.15.0 Snap 5.0

How reproducible:
Always

Steps to Reproduce:
1. Prepare Satellite for provisioning, and setup Libvirt CR
2. Sync content and kickstart repos, publish CV, create AK
3. Provision a host on Libvirt CR with cpu_mode as default

Actual results:
default cpu_mode set as host-passthrough on ComputeResource Libvirt

Expected results:
default cpu_mode set as "custom (qemu64)" earlier on ComputeResource Libvirt

Additional info:
Found this while testing this BZ and @ekohlvan@redhat.com suggested to drop this option altogether
upstream discussion - https://community.theforeman.org/t/drop-cpu-type-option-from-libvirt-compute-resource-provisioning/36267

QE Tracker for https://issues.redhat.com/browse/SAT-22491
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2258481