[Enhancement] Revert the output order requirement for Agg

**What is the bug?**
https://github.com/opensearch-project/sql/issues/3403 mentioned there are 3 differences between V2 and Calcite of aggregation results

We will keep alignment for (1) and (3), rather than all of them.
For 2, the result ordering is enforced by pushdown, so V2 engine itself doesn't sort the result by by-expressions.

So we need to revert the changes for (2)
