GH-1473: Revert CompletableFuture Changes

See #1473
See #1480

- caused problems with Boot auto configuration
- since 3.0 is a major release, switching to CF there is not onerous
- retain `CompletableFuture` as an async return type

Author: garyrussell

spring-amqp/src/main/java/org/springframework/amqp/core/AsyncAmqpTemplate2.java

@@ -42,9 +42,7 @@
  *
  * @author Gary Russell
  * @since 2.4
- * @deprecated in favor of {@link RabbitStreamTemplate2}.
  */
-@Deprecated
 public class RabbitStreamTemplate implements RabbitStreamOperations, BeanNameAware {
 
 	protected final LogAccessor logger = new LogAccessor(getClass()); // NOSONAR