message: Change the mac factory to use GetPrimitive instead of wrapping it by itself.
  This is simpler (and in all other factories it already is like this).
  GitOrigin-RevId:
diff: @@ -29,7 +29,12 @@ namespace tink {
  // static
  util::StatusOr<std::unique_ptr<Mac>> MacFactory::GetPrimitive(
  const KeysetHandle& keyset_handle) {
  - return GetPrimitive(keyset_handle, nullptr);
  + util::Status status =
  + Registry::RegisterPrimitiveWrapper(absl::make_unique<MacWrapper>());
  + if (!status.ok()) {
  + return status;
  + }
  + return keyset_handle.GetPrimitive<Mac>();
  }
  // static
  @@ -41,11 +46,7 @@ util::StatusOr<std::unique_ptr<Mac>> MacFactory::GetPrimitive(
  if (!status.ok()) {
  return status;
  }
  - auto primitives_result = keyset_handle.GetPrimitives<Mac>(custom_key_manager);
  - if (!primitives_result.ok()) {
  - return primitives_result.status();
  - }
  - return Registry::Wrap<Mac>(std::move(primitives_result.ValueOrDie()));
  + return keyset_handle.GetPrimitive<Mac>(custom_key_manager);
  }
  } // namespace tink
  