scsi: libsas: remove unused port_gone_completion and DISCE_PORT_GONE

No one uses the port_gone_completion in struct asd_sas_port and
DISCE_PORT_GONE in enum disover_event, clean them out.
Signed-off-by: Jason Yan <yanaijie@huawei.com>
CC: Johannes Thumshirn <jthumshirn@suse.de>
CC: Ewan Milne <emilne@redhat.com>
CC: Christoph Hellwig <hch@lst.de>
CC: Tomas Henzl <thenzl@redhat.com>
CC: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

include/scsi/libsas.h

@@ -81,7 +81,6 @@ enum phy_event {
 enum discover_event {
 	DISCE_DISCOVER_DOMAIN   = 0U,
 	DISCE_REVALIDATE_DOMAIN,
-	DISCE_PORT_GONE,
 	DISCE_PROBE,
 	DISCE_SUSPEND,
 	DISCE_RESUME,
@@ -256,8 +255,6 @@ struct sas_discovery {
 /* The port struct is Class:RW, driver:RO */
 struct asd_sas_port {
 /* private: */
-	struct completion port_gone_completion;
-
 	struct sas_discovery disc;
 	struct domain_device *port_dev;
 	spinlock_t dev_list_lock;