chore(proxy): update vendored postgres libs to edition 2021 (#10139)

I ran `cargo fix --edition` in each project prior, and it found nothing
that needed fixing.

libs/proxy/postgres-protocol2/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "postgres-protocol2"
 version = "0.1.0"
-edition = "2018"
+edition = "2021"
 license = "MIT/Apache-2.0"
 
 [dependencies]

libs/proxy/postgres-protocol2/src/lib.rs

@@ -9,8 +9,7 @@
 //!
 //! This library assumes that the `client_encoding` backend parameter has been
 //! set to `UTF8`. It will most likely not behave properly if that is not the case.
-#![doc(html_root_url = "https://docs.rs/postgres-protocol/0.6")]
-#![warn(missing_docs, rust_2018_idioms, clippy::all)]
+#![warn(missing_docs, clippy::all)]
 
 use byteorder::{BigEndian, ByteOrder};
 use bytes::{BufMut, BytesMut};

libs/proxy/postgres-protocol2/src/message/frontend.rs

@@ -3,7 +3,6 @@
 
 use byteorder::{BigEndian, ByteOrder};
 use bytes::{Buf, BufMut, BytesMut};
-use std::convert::TryFrom;
 use std::error::Error;
 use std::io;
 use std::marker;