Make s-c-function deployer optional dependency

spring-cloud-stream-binder-rabbit/pom.xml

@@ -18,6 +18,7 @@
 			<groupId>org.springframework.cloud</groupId>
 			<artifactId>spring-cloud-function-deployer</artifactId>
 			<version>${spring-cloud-function.version}</version>
+			<optional>true</optional>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.cloud</groupId>

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

@@ -217,6 +217,10 @@ public class RabbitMessageChannelBinder extends
 		this.decompressingPostProcessor = decompressingPostProcessor;
 	}
 
+	public String getProtocolIdentifier() {
+		return "amqp";
+	}
+
 	/**
 	 * Set a {@link org.springframework.amqp.core.MessagePostProcessor} to compress
 	 * messages. Defaults to a