GH-1145: Remove destroying producer factory

Remove the un-ncessary call to destroy the producer when checking for partitions.
This way, the producer is cached and reused at the first time data is produced.

Resolves https://github.com/spring-cloud/spring-cloud-stream-binder-kafka/issues/1145

spring-cloud-stream-binder-kafka/src/main/java/org/springframework/cloud/stream/binder/kafka/KafkaMessageChannelBinder.java

@@ -399,9 +399,6 @@ public class KafkaMessageChannelBinder extends
 					List<PartitionInfo> partitionsFor = producer
 							.partitionsFor(destination.getName());
 					producer.close();
-					if (transMan == null) {
-						((DisposableBean) producerFB).destroy();
-					}
 					return partitionsFor;
 				}, destination.getName());
 		this.topicsInUse.put(destination.getName(),