Change default value of tidb_remove_orderby_in_subquery to true

[elsa0520]

Enhancement

Change the default value tidb_remove_orderby_in_subquery to true.
It will not change the behaviors of upgrade cluster.
It just change the behaviors of new cluster after v7.2

Example

1. create table

CREATE TABLE `t1` ( `a` int(11) DEFAULT NULL, `b` int(11) DEFAULT NULL, `c` int(11) DEFAULT NULL);

2. explain query
   without order by plan node

"TableReader 10000.00 root  data:TableFullScan",
			"└─TableFullScan 10000.00 cop[tikv] table:t1 keep order:false, stats:pseudo"