scsi: remove tsk_mgmt_response and it_nexus_response transport methods

They are never called and just dispatch to methods of the same names in
the FC and SRP transport classes that are never implemented.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>