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>

backends/iommufd.c

@@ -80,11 +80,6 @@ int iommufd_backend_connect(IOMMUFDBackend *be, Error **errp)
     int fd, ret = 0;
 
     qemu_mutex_lock(&be->lock);
-    if (be->users == UINT32_MAX) {
-        error_setg(errp, "too many connections");
-        ret = -E2BIG;
-        goto out;
-    }
     if (be->owned && !be->users) {
         fd = qemu_open_old("/dev/iommu", O_RDWR);
         if (fd < 0) {