Reverts llvm/llvm-project#184440 Furo seems to parse the entire navtree HTML blob for every page, and the navtree is large, so now doc building takes > 25min. I wasn't able to fix forward, so let's roll back for now. Agent analysis here: https://gist.github.com/rnk/5e26e09fbf1f51a501e6ab4139d048ad