backends/iommufd: Remove check on number of backend users

QOM already has a ref count on objects and it will assert much
earlier, when INT_MAX is reached.

Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
1 file changed