MDEV-24779: main.subselect fails in buildbot with --ps-protocol

Follow-up fix to commit 26f50335(MDEV-23449)
The GROUP BY clause inside IN/ALL/ANY subquery is removed
when there is no aggregate function or HAVING clause in the subquery.

When the GROUP BY clause is removed, a subquery can also be removed
if it part of the GROUP BY clause. This is done inside the function
remove_redundant_subquery_clauses. Here we walk over the GROUP BY list
and remove a subselect from its unit via the callback function
eliminate_subselect_processor.

The issue here was that when the query was being re-executed it was trying
to reinitialize the select that was removed as stated above.
This is not required, so the fix would be to remove select_lex
both from tree lex structure and the global list of nodes so that
we don't do the reinitialization again.

mysql-test/r/ps.result

@@ -5390,5 +5390,17 @@ ERROR HY000: Default/ignore value is not supported for such parameter usage
 EXECUTE IMMEDIATE 'SHOW DATABASES WHERE ?' USING 0;
 Database
 #
+# MDEV-24779: main.subselect fails in buildbot with --ps-protocol
+#
+CREATE TABLE t1(a INT);
+PREPARE stmt FROM "SELECT EXISTS(SELECT 1 FROM t1 GROUP BY a IN (select a from t1))";
+EXECUTE stmt;
+EXISTS(SELECT 1 FROM t1 GROUP BY a IN (select a from t1))
+0
+EXECUTE stmt;
+EXISTS(SELECT 1 FROM t1 GROUP BY a IN (select a from t1))
+0
+DROP TABLE t1;
+#
 # End of 10.2 tests
 #

mysql-test/t/ps.test

@@ -4902,6 +4902,16 @@ DROP TABLE t1;
 EXECUTE IMMEDIATE 'SHOW DATABASES WHERE ?' USING DEFAULT;
 EXECUTE IMMEDIATE 'SHOW DATABASES WHERE ?' USING 0;
 
+--echo #
+--echo # MDEV-24779: main.subselect fails in buildbot with --ps-protocol
+--echo #
+
+CREATE TABLE t1(a INT);
+PREPARE stmt FROM "SELECT EXISTS(SELECT 1 FROM t1 GROUP BY a IN (select a from t1))";
+EXECUTE stmt;
+EXECUTE stmt;
+DROP TABLE t1;
+
 --echo #
 --echo # End of 10.2 tests
 --echo #

sql/item_subselect.cc

@@ -368,7 +368,7 @@ bool Item_subselect::mark_as_eliminated_processor(void *arg)
 bool Item_subselect::eliminate_subselect_processor(void *arg)
 {
   unit->item= NULL;
-  unit->exclude_from_tree();
+  unit->exclude();
   eliminated= TRUE;
   return FALSE;
 }