GH-2292: Doc - Fix Container Factory Generics

Resolves #2292

Author: garyrussell

Diff for: spring-kafka-docs/src/main/asciidoc/kafka.adoc

@@ -1511,7 +1511,7 @@ The following example shows how to do so:
 [source, java]
 ----
 @Bean
-public KafkaListenerContainerFactory<?, ?> batchFactory() {
+public KafkaListenerContainerFactory<?> batchFactory() {
     ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
             new ConcurrentKafkaListenerContainerFactory<>();
     factory.setConsumerFactory(consumerFactory());
@@ -3272,7 +3272,7 @@ Starting with version 2.3.4, you can add a `ContainerCustomizer` to the factory
 [source, java]
 ----
 @Bean
-public KafkaListenerContainerFactory<?, ?> kafkaListenerContainerFactory() {
+public KafkaListenerContainerFactory<?> kafkaListenerContainerFactory() {
     ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
             new ConcurrentKafkaListenerContainerFactory<>();
     ...
@@ -4248,7 +4248,7 @@ The following example shows how to do so:
 [source, java]
 ----
 @Bean
-public KafkaListenerContainerFactory<?, ?> kafkaJsonListenerContainerFactory() {
+public KafkaListenerContainerFactory<?> kafkaJsonListenerContainerFactory() {
     ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
         new ConcurrentKafkaListenerContainerFactory<>();
     factory.setConsumerFactory(consumerFactory());
@@ -4480,7 +4480,7 @@ The following example creates beans that use this method:
 [source, java]
 ----
 @Bean
-public KafkaListenerContainerFactory<?, ?> kafkaListenerContainerFactory() {
+public KafkaListenerContainerFactory<?> kafkaListenerContainerFactory() {
     ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
             new ConcurrentKafkaListenerContainerFactory<>();
     factory.setConsumerFactory(consumerFactory());