Rollup merge of #133930 - chriskrycho:mdbook-trpl-package, r=ehuss

rustbook: update to use new mdbook-trpl package from The Book

Updates to the latest merge from `rust-lang/book` and simplifies the dependency chain there. There are now three preprocessors, but only one package, so everything is a lot nicer to deal with from the consuming POV (i.e. here).

Author: matthiaskrgr