sanlock: UNUSED flag for lockspace rem
    
    salock_rem_lockspace(UNUSED) will return -EBUSY
    if any resources exist for the given lockspace,
    instead of forcibly removing the lockspace by
    killing any pids using resources within the
    lockspace, and then removing the lockspace once
    all resources are gone.
    
    Signed-off-by: David Teigland <teigland@redhat.com>