Remove dead code for encoding/decoding lint IDs
Remove dead code for encoding/decoding lint IDs

This helps decouple the lint system from needing the implicit TLS TyCtxt
as well.

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust