As we prepare to clarify how conversions are treated, we don't want a
`sink(...)` declaration where it's non-obvious which conversions are
applied to arguments.
This sort of fixes one FP and causes a new FN, but for the wrong reasons. The IR dataflow is tracking the reference itself, rather than the referred-to object. Once we can better model indirections, we can make this work correctly.
This change is still the right thing to do, because it ensures that the dataflow is looking at actual expression being computed by the instruction.
