Minor improvement to save some testing runtime (~ 2 minutes).

Reason:
   This test executes DML statements on a NDB table to detect if some SQL statements of special interest commits the ongoing transaction.
   When running in MIXED mode, automatic switching from statement-based to row-based replication takes place when a DML statement
   updates an NDB table.
   That means running this test on NDB with binlog-format=mixed and binlog-format=row mostly checks the same routines twice.
   Therefore we skip the variant with binlog-format=mixed.

mysql-test/t/rpl_ndb_ddl.test

@@ -24,7 +24,7 @@
 #
 
 --source include/master-slave.inc
---source include/have_binlog_format_mixed_or_row.inc
+--source include/have_binlog_format_row.inc
 --source include/have_ndb.inc
 let $engine_type= NDB;
 let $temp_engine_type= MEMORY;