MDEV-7215 EXPLAIN REPLACE produces an error: Column count doesn't match value count

removed outdated code which was causing error (no need reassign result for subqueries & Co)

mysql-test/r/explain.result

@@ -393,3 +393,17 @@ Warnings:
 Note	1003	select NULL AS `a` from (select NULL AS `a` from `test`.`t1` where 0) `t`
 set optimizer_switch=@tmp_optimizer_switch;
 DROP TABLE t1,t2;
+#
+# MDEV-7215: EXPLAIN REPLACE produces an error:
+# Column count doesn't match value count 
+#
+create table t1 (a int);
+insert into t1 values (1);
+create table t2 (b int, c int);
+replace into t2 select 100, (select a from t1);
+explain replace into t2 select 100, (select a from t1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	PRIMARY	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+2	SUBQUERY	t1	system	NULL	NULL	NULL	NULL	1	
+drop table t1, t2;
+# End of 10.1 tests

mysql-test/t/explain.test

@@ -317,3 +317,19 @@ SELECT * FROM ( SELECT t1.a FROM t1,t2 WHERE t2.a = t1.a ) AS t;
 set optimizer_switch=@tmp_optimizer_switch;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-7215: EXPLAIN REPLACE produces an error:
+--echo # Column count doesn't match value count 
+--echo #
+create table t1 (a int);
+insert into t1 values (1);
+create table t2 (b int, c int);
+
+replace into t2 select 100, (select a from t1);
+explain replace into t2 select 100, (select a from t1);
+#analyze replace into t2 select 100, (select a from t1);
+
+drop table t1, t2;
+
+--echo # End of 10.1 tests

sql/sql_select.cc

@@ -3249,11 +3249,6 @@ mysql_select(THD *thd, Item ***rref_pointer_array,
     {
       if (select_lex->linkage != GLOBAL_OPTIONS_TYPE)
       {
-	//here is EXPLAIN of subselect or derived table
-	if (join->change_result(result))
-	{
-	  DBUG_RETURN(TRUE);
-	}
         /*
           Original join tabs might be overwritten at first
           subselect execution. So we need to restore them.