The purpose of this class was to avoid reporting conflicting JVM
signatures / accidental override errors when there's a similar (e.g.
conflicting overloads) diagnostic already reported.
It was not used meaningfully because it only affected diagnostics
reported by the old JVM backend. Also, in real life, backend diagnostics
would not be reported anyway in most cases because backend is not even
run if there's an error after frontend.
Alexander Udalov
5cbaf077f3