Remove unnecessary assertion

Issue: SPR-14279

Author: rstoyanchev

spring-messaging/src/main/java/org/springframework/messaging/simp/broker/SimpleBrokerMessageHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -223,12 +223,6 @@ protected void handleMessageInternal(Message<?> message) {
 			return;
 		}
 
-		SimpMessageHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, SimpMessageHeaderAccessor.class);
-		if (accessor == null) {
-			throw new IllegalStateException(
-					"No header accessor (not using the SimpMessagingTemplate?): " + message);
-		}
-
 		if (SimpMessageType.MESSAGE.equals(messageType)) {
 			logMessage(message);
 			sendMessageToSubscribers(destination, message);