scsi: fc: drop residual tsk_mgmt_response and it_nexus_response

After commit 556e26a7 ("scsi: remove tsk_mgmt_response and
it_nexus_response transport methods"), the target driver support was
removed totally. Drop the residual.

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>