[clang] [Clang] update reasoned delete diagnostic kind to use Extension, making it pedantic only (PR #114713)

[Oleksandr T. via cfe-commits]

a-tarasyuk wrote:

> I think we should make these changes to all backported features.

@zwuis @AaronBallman is it okay to handle that in a separate issue/PR?



https://github.com/llvm/llvm-project/pull/114713