[clang] [clang] Remove FEM_Indeterminable (PR #137661)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

> @ojhunt In #137600 there are a list of a few temporary PRs that were merged in to silence the warning. These need to be reverted after this one gets merged in. Do you want to revert them or you want me to do that?

I removed them as part of resolving the merge conflict, and reverted https://github.com/swiftlang/llvm-project/commit/c2a62af2a51d58183bcd72ee8a86c37ddd526758 manually

https://github.com/llvm/llvm-project/pull/137661