[llvm] [Casting][NFC] Remove soft deprecation on functions with `_or_null` suffix (PR #218876)

[Corentin Jabot via llvm-commits]

cor3ntin wrote:

Did you look into the suggestion i made there?
https://discourse.llvm.org/t/psa-swapping-out-or-null-with-if-present/65018/14 (ie make non_null only accept pointers, and if_present work on optional)

Given we are at the start of a cycle it would be a good time to do it if we wanted to go that direction

https://github.com/llvm/llvm-project/pull/218876