block: remove the deprecated ub driver

It was scheduled to be removed in 3.6.

Acked-by: Pete Zaitcev <zaitcev@redhat.com>
Cc: Jens Axboe <jaxboe@fusionio.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>