[clang] Remove duplicate API (PR #132776)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll requested changes to this pull request.

libclang's API is called stable for a reason.
It's too late to remove anything. The best we can do is to implement one function in terms of another to avoid duplication on implementation side, and put `[[deprecated("use the other one")]]` on the one we think shouldn't be used.

https://github.com/llvm/llvm-project/pull/132776