Rollup merge of rust-lang#57463 - phansch:fix_some_links, r=steveklabnik

docs: Fix some 'second-edition' links

If I understand it correctly, we now want to link to

    https://doc.rust-lang.org/book/*.html

instead of

    https://doc.rust-lang.org/book/second-edition/*.html

because the second-edition page says that it's no longer distributed with
Rust's docs.

For example: https://doc.rust-lang.org/book/second-edition/ch13-01-closures.html