qemu: command: Stop formatting of 'scsi=off' for virtio-blk-pci

The property was deprecated. Don't format it based on the new capability
if the user didn't explicitly request it.

https://bugzilla.redhat.com/show_bug.cgi?id=1829550



Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>