ubd: remove the code to register as the legacy IDE driver

ubd: remove the code to register as the legacy IDE driver

With the legacy IDE driver long deprecated, and modern userspace being
much more flexible about dev_t assignments there is no reason to fake
a registration as the legacy IDE driver in ubd.  This registeration
is a little problematic as it registers the same request_queue for
multiple gendisks, so just remove it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Link: https://lore.kernel.org/r/20210614060759.3965724-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>