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/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;