remove assertion that covers only mocked behavior of Publish

src/test/java/com/hivemq/extensions/google/cloud/pubsub/customizations/helloworld/PubSubToMqttHelloWorldTransformerTest.java

@@ -187,7 +187,6 @@ void transformMessage_noData_metricIncreased() {
  final List<Publish> publishes = publishAtomicReference.get();
  assertNotNull(publishes);
  assertEquals(1, publishes.size());
- assertTrue(publishes.get(0).getPayload().isPresent());
  assertEquals(1, metricRegistry.counter(MISSING_DATA_COUNTER_NAME).getCount());
  }
 }