Cleaning up retry-topic-lcf.adoc

Fixes: #3084

* Remove `useLegacyFactoryConfigurer` documentation from retry-topic-lcf.adoc

(cherry picked from commit 3927d64)

Author: Wzy19930507

spring-kafka-docs/src/main/antora/modules/ROOT/pages/retrytopic/retry-topic-lcf.adoc

@@ -35,13 +35,3 @@ public RetryTopicConfiguration myOtherRetryTopic(KafkaTemplate<Integer, MyPojo>
 
 IMPORTANT: Since 2.8.3 you can use the same factory for retryable and non-retryable topics.
 
-If you need to revert the factory configuration behavior to prior 2.8.3, you can override the `configureRetryTopicConfigurer` method of a `@Configuration` class that extends `RetryTopicConfigurationSupport` as explained in xref:retrytopic/retry-config.adoc#retry-topic-global-settings[Configuring Global Settings and Features] and set `useLegacyFactoryConfigurer` to `true`, such as:
-
-[source, java]
-----
-@Override
-protected Consumer<RetryTopicConfigurer> configureRetryTopicConfigurer() {
-    return rtc -> rtc.useLegacyFactoryConfigurer(true);
-}
-----
-