sbp2: delete sbp2scsi_direction_table

DMA_BIDIRECTIONAL data direction may be handled properly by Linux in the
future.  For now, reject it instead to convert it to another direction.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jody McIntyre <scjody@modernduck.com>