BE: Chore: Fix code style in internalConsumerGroup (#3697)

Signed-off-by: nisanohana3 <nisana230@gmail.com>
Co-authored-by: Roman Zabaluev <rzabaluev@provectus.com>

kafka-ui-api/src/main/java/com/provectus/kafka/ui/model/InternalConsumerGroup.java

@@ -74,14 +74,12 @@ public class InternalConsumerGroup {
 
   private static Integer calculateTopicNum(Map<TopicPartition, Long> offsets, Collection<InternalMember> members) {
 
-    long topicNum = Stream.concat(
+    return (int) Stream.concat(
         offsets.keySet().stream().map(TopicPartition::topic),
         members.stream()
             .flatMap(m -> m.getAssignment().stream().map(TopicPartition::topic))
     ).distinct().count();
 
-    return Integer.valueOf((int) topicNum);
-
   }
 
   private static Collection<InternalMember> initInternalMembers(ConsumerGroupDescription description) {