support set names/charset and variables in one sql

src/sql/ob_sql_utils.cpp

@@ -1482,9 +1482,7 @@ bool ObSQLUtils::is_readonly_stmt(ParseResult& result)
                T_SHOW_PARAMETERS == type || T_SHOW_INDEXES == type || T_SHOW_PROCESSLIST == type ||
                T_SHOW_TABLEGROUPS == type || T_USE_DATABASE == type || T_TRANSACTION == type || T_BEGIN == type ||
                T_COMMIT == type || T_ROLLBACK == type || T_VARIABLE_SET == type ||
-               T_SET_NAMES == type       // read only not restrict it
-               || T_SET_CHARSET == type  // read only not restrict it
-               || T_SHOW_RECYCLEBIN == type || T_SHOW_TENANT == type || T_SHOW_RESTORE_PREVIEW == type) {
+               T_SHOW_RECYCLEBIN == type || T_SHOW_TENANT == type || T_SHOW_RESTORE_PREVIEW == type) {
       ret = true;
     }
   }