Update libp2p-core

[ackintosh]

Description

Update libp2p-core to the latest version so that we can remove the protoc dependency.

https://github.com/libp2p/rust-libp2p/blob/master/core/CHANGELOG.md

Notes & open questions

Notable changes of dependencies related this PR:

• libp2p_core
  • identity moved from libp2p_core::identity to libp2p_identity since 0.40.0
• multiaddr
  • Protocol::P2p contain a PeerId instead of a Multihash since 0.18.0
• libp2p_identity
  • PublicKey::from_protobuf_encoding has been renamed to PublicKey::try_decode_protobuf in 0.1.2
  • PublicKey::encode_uncompressed has been renamed to PublicKey::to_bytes_uncompressed in 0.1.2
  • PublicKey::encode has been renamed to PublicKey::to_bytes in 0.1.2
  • PublicKey has been made opaque since 0.2.0

I have tested this change with the request_enr example:

$ cargo run --all-features --example request_enr /ip4/168.119.142.133/udp/9000/p2p/16Uiu2HAm6zDun1JBzHVcX7XDPxh3sPqkhfyN7dew4J5UNWAfDEdH
ENR Found:
Base64:enr:-L64QON1kt-4lAFXbqHRn6QLaNxgplXV658zfbKuOi2WNBXiOXeX7FulKi-9IXxUPnLioTlTMuTAlmIh0R-0TDX0U5qChiSHYXR0bmV0c4gAgAEAAAAAAIRldGgykGKJQe8DABAg__________-CaWSCdjSCaXCEqHeOhYlzZWNwMjU2azGhAqvHPwzUgfAmpEikOp1Vb9TU96LExblJ-cEP7yJ1ghCsiHN5bmNuZXRzD4N0Y3CCIyiDdWRwgiMo
enr:-L64QON1kt-4lAFXbqHRn6QLaNxgplXV658zfbKuOi2WNBXiOXeX7FulKi-9IXxUPnLioTlTMuTAlmIh0R-0TDX0U5qChiSHYXR0bmV0c4gAgAEAAAAAAIRldGgykGKJQe8DABAg__________-CaWSCdjSCaXCEqHeOhYlzZWNwMjU2azGhAqvHPwzUgfAmpEikOp1Vb9TU96LExblJ-cEP7yJ1ghCsiHN5bmNuZXRzD4N0Y3CCIyiDdWRwgiMo

Change checklist

• Self-review
• Documentation updates if relevant
• Tests if relevant