scsi: smartpqi: Update deleting a LUN via sysfs

scsi: smartpqi: Update deleting a LUN via sysfs

Change removing a LUN using sysfs from an internal driver function
pqi_remove_all_scsi_devices() to using the .slave_destroy entry in the
scsi_host_template.

A LUN can be deleted via sysfs using this syntax:

echo 1 > /sys/block/sdX/device/delete

Link: https://lore.kernel.org/r/165730607154.177165.9723066932202995774.stgit@brunhilda
Reviewed-by: Scott Teel <scott.teel@microchip.com>
Reviewed-by: Mike McGowen <mike.mcgowen@microchip.com>
Signed-off-by: Kevin Barnett <kevin.barnett@microchip.com>
Signed-off-by: Don Brace <don.brace@microchip.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>