Most example code in RFCs is not written with executability in mind, so having the "Run" button available by default on all RFCs seems a bit misleading.
This now disables the playground for the whole book (which also removes the "hidden" code mdbook inserts). It thus only leaves the copy button.
This significantly shrinks the pre-compressed search index:
$ du -h searchindex-old.js searchindex-new.js
26M searchindex-old.js
19M searchindex-new.js
And shrinks the search index even after it's gzipped:
$ du -h searchindex-old.js.gz searchindex-new.js.gz
4.5M searchindex-old.js.gz
3.3M searchindex-new.js.gz
This change requires a newer version of mdBook, with
https://github.com/rust-lang/mdBook/pull/1637