AND ORDER BY IN A SUBQUERY

Issue:
------
prepare xx from
"SELECT 1 AS countSelected
FROM (SELECT 2, ........
      FROM .......
      ORDER BY (SELECT 3 .........)) AS t2
ORDER BY countSelected";

In conventional execution:
1) "SELECT 3" is removed by
   Item_singlerow_subselect::select_transformer(). This
   subquery is replaced with an Item_int.
2) "SELECT 2 ..." is invalidated as part of the
   derived_merge strategy by SELECT_LEX::merge_derived.


During Prepare:
1) "SELECT 3" can't be removed by
   Item_singlerow_subselect::select_transformer because of
   the special condition
   "thd->stmt_arena->is_stmt_prepare_or_first_sp_execute()".
   So this subquery  is not removed..

2) "SELECT 2 ..." is invalidated as part of the
   derived_merge strategy by SELECT_LEX::merge_derived.

This makes "SELECT 3" an orphan and causes incorrect
behavior during EXECUTE.

Solution:
---------
When a derived table is merged, the ORDER BY clause in the
derived table should either be moved into the outer query
block or removed.

In this case, it can't moved into the outer query since
there is already an ORDER BY clause in the outer query. So
the derived table's ORDER BY should be eliminated. This
part has now been implemented.