quic: stop guarding ngtcp2_recv_stop_sending callback field

@@ -1445,7 +1445,7 @@ class Http3ApplicationImpl final : public Session::Application {    static constexpr nghttp3_callbacks kCallbacks = {       on_acked_stream_data,-      nullptr,  // nghttp3_stream_close (deprecated)+      nullptr,  // stream_close (deprecated, use v2 below)       on_receive_data,       on_deferred_consume,       on_begin_headers,@@ -1458,7 +1458,7 @@ class Http3ApplicationImpl final : public Session::Application {       on_end_stream,       on_do_reset_stream,       on_shutdown,-      nullptr,  // recv_settings (deprecated)+      nullptr,  // recv_settings (deprecated, use v2 below)       on_receive_origin,       on_end_origin,       on_rand,

@@ -1654,7 +1654,7 @@ struct Session::Impl final : public MemoryRetainer {    static constexpr ngtcp2_callbacks CLIENT = {       ngtcp2_crypto_client_initial_cb,-      nullptr,  // stream_stop_sending+      nullptr,  // recv_client_initial       ngtcp2_crypto_recv_crypto_data_cb,       on_handshake_completed,       on_receive_version_negotiation,@@ -1688,7 +1688,7 @@ struct Session::Impl final : public MemoryRetainer {       on_acknowledge_datagram,       on_lost_datagram,       nullptr,  // get_path_challenge_data (deprecated, use v2 below)-      nullptr,  // stream_stop_sending+      nullptr,  // stream_stop_sending (deprecated, use v2 below)       ngtcp2_crypto_version_negotiation_cb,       on_receive_rx_key,       on_receive_tx_key,@@ -1698,20 +1698,18 @@ struct Session::Impl final : public MemoryRetainer {       on_get_new_cid,       on_cid_status,       ngtcp2_crypto_get_path_challenge_data2_cb,-#ifdef NGTCP2_CALLBACKS_V4       on_receive_stream_stop_sending, #ifdef NGTCP2_CALLBACKS_V5-      nullptr,-#endif  // NGTCP2_CALLBACKS_V5-#endif  // NGTCP2_CALLBACKS_V4+      nullptr,  // stream_close2+#endif   };    static constexpr ngtcp2_callbacks SERVER = {-      nullptr,  // stream_stop_sending+      nullptr,  // client_initial       ngtcp2_crypto_recv_client_initial_cb,       ngtcp2_crypto_recv_crypto_data_cb,       on_handshake_completed,-      nullptr,+      nullptr,  // recv_version_negotiation       ngtcp2_crypto_encrypt_cb,       ngtcp2_crypto_decrypt_cb,       ngtcp2_crypto_hp_mask_cb,@@ -1720,44 +1718,42 @@ struct Session::Impl final : public MemoryRetainer {       on_stream_open,       on_stream_close,       nullptr,  // recv_stateless_reset (deprecated, use v2 below)-      nullptr,+      nullptr,  // recv_retry       on_extend_max_streams_bidi,       on_extend_max_streams_uni,       on_rand,       nullptr,  // get_new_connection_id (deprecated, use v2 below)       on_remove_connection_id,       ngtcp2_crypto_update_key_cb,       on_path_validation,-      nullptr,+      nullptr,  // select_preferred_addr       on_stream_reset,       on_extend_max_remote_streams_bidi,       on_extend_max_remote_streams_uni,       on_extend_max_stream_data,       nullptr,  // dcid_status (deprecated, use v2 below)-      nullptr,-      nullptr,+      nullptr,  // handshake_confirmed+      nullptr,  // recv_new_token       ngtcp2_crypto_delete_crypto_aead_ctx_cb,       ngtcp2_crypto_delete_crypto_cipher_ctx_cb,       on_receive_datagram,       on_acknowledge_datagram,       on_lost_datagram,       nullptr,  // get_path_challenge_data (deprecated, use v2 below)-      nullptr,  // stream_stop_sending+      nullptr,  // stream_stop_sending (deprecated, use v2 below)       ngtcp2_crypto_version_negotiation_cb,-      nullptr,+      nullptr,  // recv_rx_key       on_receive_tx_key,       on_early_data_rejected,       on_begin_path_validation,       on_receive_stateless_reset,       on_get_new_cid,       on_cid_status,       ngtcp2_crypto_get_path_challenge_data2_cb,-#ifdef NGTCP2_CALLBACKS_V4       on_receive_stream_stop_sending, #ifdef NGTCP2_CALLBACKS_V5-      nullptr,-#endif  // NGTCP2_CALLBACKS_V5-#endif  // NGTCP2_CALLBACKS_V4+      nullptr,  // stream_close2+#endif   }; };