acornscsi: remove linked command support

The acornscsi driver was added in v2.1.88. It has always #undef-ed
CONFIG_SCSI_ACORNSCSI_LINK near the top of acornscsi.c. And, just to be
sure, it has also always triggered a preprocessor error if
CONFIG_SCSI_ACORNSCSI_LINK was still defined. But, as far as I can see,
it has never even been possible to set SCSI_ACORNSCSI_LINK through
kconfig, or its predecessors, in the first place.

Let's remove the code involved.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>