Remove unused member function declaration

src/h2load.h

@@ -465,8 +465,6 @@ struct Client {
   int quic_stream_close(int64_t stream_id, uint64_t app_error_code);
   int quic_stream_reset(int64_t stream_id, uint64_t app_error_code);
   int quic_extend_max_local_streams();
-  int quic_update_key(uint8_t *rx_key, uint8_t *rx_iv, uint8_t *tx_key,
-                      uint8_t *tx_iv);
 
   int quic_on_key(ngtcp2_crypto_level level, const uint8_t *rx_secret,
                   const uint8_t *tx_secret, size_t secretlen);