message: Use existing type alias
diff: @@ -669,23 +669,22 @@ Irohad::RunResult Irohad::initMstProcessor() {
  }
  Irohad::RunResult Irohad::initPendingTxsStorage() {
  - using PreparedTransactionType =
  - std::pair<shared_model::interface::types::AccountIdType,
  - shared_model::interface::types::HashType>;
  + using PreparedTransactionDescriptor =
  + PendingTransactionStorageImpl::PreparedTransactionDescriptor;
  pending_txs_storage_ = std::make_shared<PendingTransactionStorageImpl>(
  mst_processor->onStateUpdate(),
  mst_processor->onPreparedBatches(),
  mst_processor->onExpiredBatches(),
  - pcs->onProposal().flat_map(
  - [](const OrderingEvent &event)
  - -> rxcpp::observable<PreparedTransactionType> {
  + pcs->onProposal().flat_map([](const OrderingEvent &event)
  + -> rxcpp::observable<
  + PreparedTransactionDescriptor> {
  if (not event.proposal) {
  - return rxcpp::observable<>::empty<PreparedTransactionType>();
  + return rxcpp::observable<>::empty<PreparedTransactionDescriptor>();
  }
  auto prepared_transactions =
  event.proposal.get()->transactions()
  | boost::adaptors::transformed(
  - [](const auto &tx) -> PreparedTransactionType {
  + [](const auto &tx) -> PreparedTransactionDescriptor {
  return std::make_pair(tx.creatorAccountId(), tx.hash());
  });
  return rxcpp::observable<>::iterate(prepared_transactions);
  