scsi: libsas: kill useless ha_event and do some cleanup

The ha_event now has only one event HAE_RESET, and this event does
nothing. Kill it and do some cleanup.

This is a preparation for enhance libsas hotplug feature in the next
patches.

Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
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>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>