VARCHAR文档错误

[文档](http://doris.apache.org/master/zh-CN/sql-reference/sql-statements/Data%20Types/VARCHAR.html#description)介绍VARCHAR最大长度为65535，但实际应为65533
```
mysql(sduzh)> create table t0(k varchar(65535)) distributed by hash(k) buckets 1;
ERROR 1064 (HY000): errCode = 2, detailMessage = Varchar size must be <= 65533: 65535
```
