Remove test assertion on x-mqtt-dup header

It's been removed.

Author: acogoluegnes

src/test/java/com/rabbitmq/stream/impl/MqttInteroperabilityTest.java

@@ -124,6 +124,5 @@ void publishToMqttTopicConsumeFromStream() throws Exception {
         .isEqualTo(UnsignedByte.valueOf("1"));
     assertThat(message.getApplicationProperties().get("x-mqtt-publish-qos"))
         .isEqualTo(Byte.valueOf("0"));
-    assertThat(message.getApplicationProperties().get("x-mqtt-dup")).isEqualTo(Boolean.FALSE);
   }
 }