[clang] Revert counted_by attribute feature (PR #75857)

[Nathan Chancellor via cfe-commits]

nathanchance wrote:

> @nathanchance can you test this please to verify it's unbreaking the linux kernel builds?

A quick initial test shows this resolves the two cases that I found in https://github.com/llvm/llvm-project/issues/73168. I can do a fuller set of builds if necessary but since this is just backing out of `__attribute__((__counted_by__(...)))` altogether, I don't expect there to be any other issues as a result of this change (other than just uncovering other unrelated breakages from not having consistent ToT LLVM builds for almost a month in CI).

https://github.com/llvm/llvm-project/pull/75857