scsi: ibmvscsi_tgt: Remove target_wait_for_sess_cmd()

There is currently a bug with the driver where there is never a call to
target_sess_cmd_list_set_waiting(), it only called
target_wait_for_sess_cmd(), which basically means that the sess_wait_list
would always be empty.

Thus, list_empty(&sess->sess_wait_list) = true,
(eg: no se_cmd I/O is quiesced, because no se_cmd in sess_wait_list),
since commit 712db3eb

 ("scsi: ibmvscsis: Properly deregister
target sessions") in 4.9.y code.

ibmvscsi_tgt does not remove the I_T Nexus when a VM is active so we can
fix this issue by removing the call to target_wait_for_sess_cmd()
altogether.

Signed-off-by: Bryant G. Ly <bly@catalogicsoftware.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>