[llvm] [Docs][DebugInfo][RemoveDIs] Revise debug info migration guide title (PR #81480)

[Jeremy Morse via llvm-commits]

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

/me squints -- apologies, I think I wrote that under the impression that the page title would be presented as "RemoveDIs" or something like that, and didn't check once it landed.

LGTM.

https://github.com/llvm/llvm-project/pull/81480