message: don't mutate method/field refs
  Summary: This addresses a TODO in the code, and is apparently truely not needed anymore.
diff: @@ -327,8 +327,6 @@ void change_visibility(IRCode* code,
  if (field != nullptr && field->is_concrete()) {
  set_public(field);
  set_public(type_class(field->get_class()));
  - // FIXME no point in rewriting opcodes in the method
  - insn->set_field(field);
  }
  } else if (insn->has_method()) {
  auto cls = type_class(insn->get_method()->get_class());
  @@ -345,8 +343,6 @@ void change_visibility(IRCode* code,
  if (cls != nullptr && !cls->is_external()) {
  set_public(cls);
  }
  - // FIXME no point in rewriting opcodes in the method
  - insn->set_method(current_method);
  }
  } else if (insn->has_type()) {
  auto type = insn->get_type();
  