[llvm] [MemProf] Remove unused declaration (NFC) (PR #173323)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

Looks like the declaration was added in #114465 but never actually implemented or called anywhere.

Drive-by LGTM for the cleanup.

https://github.com/llvm/llvm-project/pull/173323