Always use classic engine for IDhack plans

As part of the SBE Plan Cache project we tried various optimization to improve the performance of the IDhack queries but were not able to catch up with the classic cache which has a special fast path for generating IDhack plans, which are very simple and very cheap to generate performance wise. To recover the query latency for IDhack plans with the SBE engine turned on as the default we decided to reply on the fall back mechanism and execute these queries with the classic engine. In the future we should revisit this issue and find a proper solution for how to reduce query latency for IDhack queries in SBE.