Reverts#532

While I doubt rust-postgres/postgres-types willaccept my PR anytime soon, I realized forking individual crates and adding support to them in-crate is subpar compared to just forking rust-postgres/postgres-types itself, as shortly after my first PR I started getting confusing cyclic dependency errors due to patching so many individual crates, notably withsmol_str which rkyv also brings in if enabled. It feels kind of wrong to include this feature in the massive 0.8 release when it may be superseded later.

I sincerely apologize for the inconsistency/indecisiveness of this.