GH-1829 Add 'multiplex' consumer property to the doc

Fix javadoc by removing the note about users not being expected to set this property

Resolves #1829

docs/src/main/asciidoc/spring-cloud-stream.adoc

@@ -1861,6 +1861,10 @@ Also, when native encoding and decoding is used, the `headerMode=embeddedHeaders
 See the producer property `useNativeEncoding`.
 +
 Default: `false`.
+multiplex::
+When set to true, the underlying binder will natively multiplex destinations on the same input binding.
++
+Default: `false`.
 
 ==== Advanced Consumer Configuration
 

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

@@ -155,8 +155,7 @@ public class ConsumerProperties {
 	 * By default this property is set to `false` and the binder will individually bind
 	 * each destinations in case of a comma separated multi destination list. The
 	 * individual binder implementations that need to support multiple input bindings
-	 * natively (multiplex) can enable this property. Under normal circumstances, the end
-	 * users are not expected to enable or disable this property directly.
+	 * natively (multiplex) can enable this property.
 	 */
 	private boolean multiplex;