Update sql-statement-add-index.md (#5615)

Author: Joyinqin

sql-statements/sql-statement-add-index.md

@@ -121,7 +121,6 @@ mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
 ## MySQL compatibility
 
 * `FULLTEXT`, `HASH` and `SPATIAL` indexes are not supported.
-* `VISIBLE/INVISIBLE` index is not supported (currently only the master branch actually supports this feature).
 * Descending indexes are not supported (similar to MySQL 5.7).
 * Adding multiple indexes at the same time is currently not supported.
 * Adding the primary key of the `CLUSTERED` type to a table is not supported. For more details about the primary key of the `CLUSTERED` type, refer to [clustered index](/clustered-indexes.md).