[doc] incorrect statement regarding concurrentStoreAndDispatchQueues in broker persistence guide.

The doc on Concurrent Store and Dispatch says:

The serialized configuration results in a slower performance for the broker, but it also eliminates the risk of losing messages in the event of a system failure.

This seems to be incorrect, we don't risk to loose messages as per Dejan's comment:

we don’t risk losing messages in concurrent store and dispatch scenario. We won’t return producer ack back to the producer until the the message is either in the store or has been consumed by the consumer.

Lets get this sentence removed.