[clang] [CMake]Fully delete the deprecated LLVM_USE_CRT* (PR #66850)

[Martin Storsjö via cfe-commits]

https://github.com/mstorsjo approved this pull request.

LGTM, thanks. (But let's wait with landing it until e.g. tomorrow, in case someone else has comments on it.)

https://github.com/llvm/llvm-project/pull/66850