Function send_unsubscribe 

fn send_unsubscribe(
    filters: &[TopicFilterBuf],
    queued_tx: Option<Sender<Result<(), Error>>>,
    completion_tx: Sender<Result<Vec<ReasonCode>, Error>>,
    client: &mut Client<JournaledSession>,
    pending: &mut Pending,
    queued_waiting: &mut Vec<Sender<Result<(), Error>>>,
)