cpu_x86: Promote added/removed from ancestor

cpu_x86: Promote added/removed from ancestor

When a CPU model is defined based on another model, we were completely
ignoring features marked as added to or removed from the original model
after it was released. For added features this is the right thing to do
as it will promote them to become normal features included in the new
model. But features marked as removed would become included in the new
model as well. We need to explicitly remove them as if they were never
included in the model.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>