[media] media/usbvision: remove ctrl_urb_wq

While the wakeup path seems to be set up, this waitqueue is actually
never used as no-one enqueues themselves on the list. As such, wakeups
are meaningless without waiters, so lets just get rid of the whole
thing.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>