There's no requirement that we mark every unused variable this way. I honestly don't think it's worthwhile. This warning is particularly annoying especially because of how it interacts with things where the function signature has optional requirements. If we're actually going to require this be the case, then it must be required universally and automatically checked in my opinion.

Historically this was checked via lint.  I'm not sure __unused is universal.
The other way to mark this is with _NOTE(ARGUNUSED(tz)) which is what I prefer, because we have compiler logic that does the right thing here, but if your compiler lacks it, then it gets elided from the code.