usb-storage: Drop not needed "allow_hotplug = 0"

Drop useless hack that disables hotplug on bus, after backend
storage was added to it, by setting "allow_hotplug = 0". Even
if bus is hotpluggable, it won't be possible to add another
SCSI device to bus since its realize will fail early with
error "no free target" in scsi_qdev_realize() method.
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

hw/usb/dev-storage.c

@@ -632,7 +632,6 @@ static void usb_msd_realize_storage(USBDevice *dev, Error **errp)
         error_propagate(errp, err);
         return;
     }
-    s->bus.qbus.allow_hotplug = 0;
     usb_msd_handle_reset(dev);
 
     if (bdrv_key_required(bs)) {