message: transport: Remove unused data member in Connection
diff: @@ -228,7 +228,6 @@ pub struct Connection {
  generators: Vec<Box<FrameGenerator>>,
  idle_timeout: Option<Instant>,
  indexes: StreamIndexes,
  - highest_stream: Option<u64>,
  connection_ids: HashMap<u64, (Vec<u8>, [u8; 16])>, // (sequence number, (connection id, reset token))
  send_streams: BTreeMap<StreamId, SendStream>,
  recv_streams: BTreeMap<StreamId, RecvStream>,
  @@ -374,7 +373,6 @@ impl Connection {
  acks: AckTracker::default(),
  idle_timeout: None,
  indexes: StreamIndexes::new(),
  - highest_stream: None,
  connection_ids: HashMap::new(),
  send_streams: BTreeMap::new(),
  recv_streams: BTreeMap::new(),
  