[clang] [Clang] Remove `[[carries_dependency]]` (PR #219912)

[Aaron Ballman via cfe-commits]

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

LGTM, this makes me very happy to finally see get across the finish line.

FWIW, there was a concern raised on the previous PR from Richard:

> Until or unless a C++ DR permits us to define __has_cpp_attribute(carries_dependency) to any value other than 200809L, we have a conformance requirement to macro-expand this to that value.

This conformance requirement was changed by p2552r3 being adopted as a DR because that paper allows `__has_cpp_attribute` to report `0` even for standard attributes. So it's fine for us to remove the attribute entirely and report `0` in older language modes.

https://github.com/llvm/llvm-project/pull/219912