message: Simplify List::verify_in_transaction()
  This threw a pointlessly different exception from other write transaction
  checks that made things a little awkward to test.
diff: @@ -138,9 +138,7 @@ void List::verify_attached() const
  void List::verify_in_transaction() const
  {
  verify_attached();
  - if (!m_realm->is_in_transaction()) {
  - throw InvalidTransactionException("Must be in a write transaction");
  - }
  + m_realm->verify_in_write();
  }
  size_t List::size() const
  