[llvm] [IR][NFC] Remove unused helpers for inserting dbg intrinsics (PR #212304)

[Jeremy Morse via llvm-commits]

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

(Was away sorry); LGTM, if this leads to serious pain then we can just add the functions back. Gently removing these things is helpful to flush out any further users of debug intrinsics out there; and shape what kind of support LLVM needs to provide for that.

Thanks for the cleanup!

https://github.com/llvm/llvm-project/pull/212304