This bug manifested itself for INSERT...SELECT and DELETE statements whose
WHERE condition used an IN/ANY/ALL predicand or a EXISTS predicate with
such grouping subquery that:
 - its GROUP BY clause could be eliminated,
 - the GROUP clause contained a subquery over a mergeable derived table
   referencing the updated table.

The bug ultimately caused a server crash when the prepare phase of the
statement processing was executed. This happened after removal redundant
subqueries used in the eliminated GROUP BY clause from the statement tree.
The function that excluded the subqueries from the did not do it properly.
As a result the specification of any derived table contained in a removed
subquery was not marked as excluded.

Approved by Oleksandr Byelkin <sanja@mariadb.com>