Don't raise errors for the events larger than max-message-bytes

[flowbehappy]

Currently, TiCDC use max-message-bytes for two usages:

1. To be the max batch size during batching multiple events into one message before sending to Kafka
2. Stop message larger than max-message-bytes being sent to Kafka. CDC raises an error if a message is larger, e.g. Single message is too large for avro.

While, in fact, those two usages should be set separately, instead of relying on one single setting. Because a user could send a single event with larger size.

And since there is already a message.max.bytes in the Kafka topic setting or Kafka Broker setting, we don't need to limit the message size on TiCDC any more. So I suggest we simply remove the second usage of max-message-bytes from TiCDC.

[flowbehappy]

https://docs.pingcap.com/tidb/stable/ticdc-sink-to-kafka/#configure-sink-uri-for-kafka
Don't forget to update the doc after this issue resolved.

[3AceShowHand]

ref http://github.com/pingcap/docs-cn/pull/21832