message: Clean up GetKeysetInfo() implementation internals
diff: @@ -219,16 +219,16 @@ crypto::tink::util::StatusOr<uint32_t> KeysetHandle::AddToKeyset(
  KeysetInfo KeysetHandle::GetKeysetInfo() const {
  auto& keyset = get_keyset();
  - auto keyset_info = absl::make_unique<KeysetInfo>();
  - keyset_info->set_primary_key_id(keyset.primary_key_id());
  + KeysetInfo keyset_info;
  + keyset_info.set_primary_key_id(keyset.primary_key_id());
  for (const Keyset::Key& key : keyset.key()) {
  - auto* key_info = keyset_info->add_key_info();
  + auto* key_info = keyset_info.add_key_info();
  key_info->set_key_id(key.key_id());
  key_info->set_type_url(key.key_data().type_url());
  key_info->set_output_prefix_type(key.output_prefix_type());
  key_info->set_status(key.status());
  }
  - return KeysetInfo(*keyset_info);
  + return keyset_info;
  }
  KeysetHandle::KeysetHandle(Keyset keyset)
  