Foreman offers 3 modes for the libvirt CPU model (which Foreman calls CPU mode):

• default
• host-model
• host-passthrough

Since https://github.com/fog/fog-libvirt/commit/7a3a46b48fe7387585eead28396b2ad8d29d1567 that default is host-passthrough (SAT-22491). The host-model option isn't of that much use so it makes sense to simplify it and drop the whole option. https://community.theforeman.org/t/drop-cpu-type-option-from-libvirt-compute-resource-provisioning/36267 was opened upstream.