[clang-tools-extra] [clangd] Remove the unused AST-based code folding Implementation. (PR #166189)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 commented:

cc @aketchum15 since you brought up the possibility of using this AST folding code again in [this Discourse thread](https://discourse.llvm.org/t/clangd-implementing-more-folding-ranges-and-the-pseudo-parser/86626). Do you have any short-term plans to do so?

If not, I'd say we can go ahead with this removal for now, and we can always bring it back later if we decide.

https://github.com/llvm/llvm-project/pull/166189