scsi_debug: ignore host lock option

Remove logic to optionally hold host_lock while each command is
queued. Keep module and sysfs host_lock parameters for backward
compatibility. Note in module parameter description that host_lock is
ignored.

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Hannes Reinicke <hare@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>