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/20210228055645.22253-10-chaitanya.kulkarni@wdc.comReviewed-by: Mike Christie <michael.christie@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/iscsi/iscsi_target_stat.c

@@ -28,7 +28,6 @@
 /* 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