[llvm] [X86] Delete Profile Guided Prefetch Passes (PR #167317)

[Mircea Trofin via llvm-commits]

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

LGTM, but please reference https://discourse.llvm.org/t/memory-prefetching-support-in-llvm/74078 and discourse.llvm.org/t/rfc-code-prefetch-insertion/88668. The former to support "turned down". The latter (and, btw, if there are other links relevant to the latter, please add) to support the statement about PLO optimizers (albeit the RFC I referenced is about _code_ not data, but the idea holds)

https://github.com/llvm/llvm-project/pull/167317