Fix pungi call with extra argument
    
    The script gets a label as a command line argument, and this is manually
    handled by adding it as `--label=$1` to the pungi-koji command. We
    should not add this argument to another time.
    
    This avoid problem with Pungi 4.1.17 which reports an error when seeing
    unknown arguments (which were silently ignored before).
    
    Fixes: https://pagure.io/pungi/issue/682
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>