chore(doc): Remove outdated document about prost (#2373)

Author: tottoto

tonic/src/codec/mod.rs

@@ -1,7 +1,6 @@
 //! Generic encoding and decoding.
 //!
-//! This module contains the generic `Codec`, `Encoder` and `Decoder` traits
-//! and a protobuf codec based on prost.
+//! This module contains the generic `Codec`, `Encoder` and `Decoder` traits.
 
 mod buffer;
 pub(crate) mod compression;

tonic/src/lib.rs

@@ -69,7 +69,6 @@
 //! [gRPC]: https://grpc.io
 //! [`tonic`]: https://github.com/hyperium/tonic
 //! [`tokio`]: https://docs.rs/tokio
-//! [`prost`]: https://docs.rs/prost
 //! [`hyper`]: https://docs.rs/hyper
 //! [`tower`]: https://docs.rs/tower
 //! [`tonic-build`]: https://docs.rs/tonic-build