scsi: target: iscsi: Remove unused macro ISCSI_INST_LAST_FAILURE_TYPE

Remove unused macro to fix the following compilation warning:

drivers/target//iscsi/iscsi_target_stat.c:31: warning: macro "ISCSI_INST_LAST_FAILURE_TYPE" is not used [-Wunused-macros]
#define ISCSI_INST_LAST_FAILURE_TYPE 0

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Mike Christie <[e-mail]>
Reviewed-by: Johannes Thumshirn <[e-mail]>
Signed-off-by: Chaitanya Kulkarni <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/target/iscsi/iscsi_target_stat.c

···
 /* Instance Attributes Table */
 #define ISCSI_INST_NUM_NODES		1
 #define ISCSI_INST_DESCR		"Storage Engine Target"
-#define ISCSI_INST_LAST_FAILURE_TYPE	0
 #define ISCSI_DISCONTINUITY_TIME	0
 
 #define ISCSI_NODE_INDEX		1