Remove function composition from the catalog interface

Should be easy enoug hto add back later, but it was causing issues
with type conversion where we are npot yet sophisticated enough
to chain functions together and keep track of the types being
passed between them.

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamConfiguration.java

@@ -48,10 +48,7 @@ public class StreamConfiguration {
 	@ConditionalOnProperty("spring.cloud.stream.bindings.input.destination")
 	public AbstractFunctionInvoker<?, ?> invoker(FunctionCatalog registry) {
 		String name = properties.getName();
-		Function<Flux<Object>, Flux<Object>> function = (name.indexOf(',') == -1)
-				? registry.lookupFunction(name)
-				: registry.composeFunction(
-						StringUtils.commaDelimitedListToStringArray(name));
+		Function<Flux<Object>, Flux<Object>> function = registry.lookupFunction(name);
 		return new StreamListeningFunctionInvoker(function);
 	}