MINOR: Remove unnecessary checks in TopicDelta (#20337)

field `directories` has already been validated in the constructor,so
there’s no need to check for null.


https://github.com/apache/kafka/blob/7d2ad185206cd4c7089fceb07f9a3f2c016f38d6/metadata/src/main/java/org/apache/kafka/metadata/PartitionRegistration.java#L221

Reviewers: Chia-Ping Tsai <[email protected]>, TengYao Chi
<[email protected]>, Yung <[email protected]>, Ken Huang
<[email protected]>

Author: gongxuanzhang

metadata/src/main/java/org/apache/kafka/image/TopicDelta.java

@@ -211,11 +211,7 @@ public LocalReplicaChanges localChanges(int brokerId) {
 
             try {
                 PartitionRegistration prevPartition = image.partitions().get(entry.getKey());
-                if (
-                        prevPartition == null ||
-                        prevPartition.directories == null ||
-                        prevPartition.directory(brokerId) != entry.getValue().directory(brokerId)
-                ) {
+                if (prevPartition == null || prevPartition.directory(brokerId) != entry.getValue().directory(brokerId)) {
                     directoryIds.put(
                         new TopicIdPartition(id(), new TopicPartition(name(), entry.getKey())),
                         entry.getValue().directory(brokerId)