[clang] Revert "[clang-repl] Ensure clang-repl accepts all C keywords supported in all language models (#142749) (PR #142933)

[Anutosh Bhat via cfe-commits]

anutosh491 wrote:

Needed a revert as we added a test for running `_Float16` with clang-repl only to realize later that it should be conditionally ignored for platforms such as ppc64le and AIX

https://github.com/llvm/llvm-project/pull/142933