[clang] [clang][NFC] Simplify implementation of `IgnoreExprNodes` (PR #164193)

[Victor Chernyakin via cfe-commits]

localspook wrote:

That would work, but I imagine it would be harder for the compiler to inline. I'm merging for now, but that could always be done in another PR

https://github.com/llvm/llvm-project/pull/164193