deprecate harder

We can use a magic macro to make the code throw an exception if anyone tries to use AuxElement::auxdata. We've cleaned this up already, so we don't see any errors, but this will prevent them from creeping in and provide people with early feedback if they start copying bad habits.

Potential drawback is that this could cause issues updating to a newer release if some tools in Athena headers use auxdata, but realistically this is unlikely, both because most code won't be exposed in headers and because we're so aggressively removing auxdata from Athena.