scsi: target/core: Remove the write_pending_status() callback function

Due to the patch that makes TMF handling synchronous the
write_pending_status() callback function is no longer called.  Hence remove
it.

Acked-by: Felipe Balbi <balbi@ti.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Reviewed-by: Andy Grover <agrover@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Himanshu Madhani <himanshu.madhani@qlogic.com>
Cc: Quinn Tran <quinn.tran@qlogic.com>
Cc: Saurav Kashyap <saurav.kashyap@qlogic.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>