Don't resend messages when splitting up batches

[dorner]

DB Producer has a feature where, when the batch is too large and gets rejected by Kafka, it splits the batch up and tries again. This is fine when going from the full batch to smaller batches, but when splitting it up further, it may be resending messages unnecessarily:

• Batch of 1000 gets split up into 10 batches of 100 of varying size
• The first 5 batches get sent, but the 6th one is too large
• DB Producer splits the original batch back up into 100 batches of 10 each, including the first 500 messages

These messages shouldn't be resent.