Revert "dm: usb: Use device_unbind_children to clean up usb devs on stop"

This reverts commit 6cda3695.

We want to avoid having the USB stack rely on unbind.
Signed-off-by: NSimon Glass <sjg@chromium.org>

drivers/usb/host/usb-uclass.c

@@ -158,9 +158,6 @@ int usb_stop(void)
 		ret = device_remove(bus);
 		if (ret && !err)
 			err = ret;
-		ret = device_unbind_children(bus);
-		if (ret && !err)
-			err = ret;
 	}
 
 #ifdef CONFIG_SANDBOX