[hotfix][cdc-rumtime][minor] Clean up useless code in BinaryRecordDat…

…aSerializer (apache#2845)

Co-authored-by: xuyu <[email protected]>

flink-cdc-runtime/src/main/java/com/ververica/cdc/runtime/serializer/data/binary/BinaryRecordDataSerializer.java

@@ -96,7 +96,6 @@ public BinaryRecordData deserialize(BinaryRecordData reuse, DataInputView source
                 segments == null || (segments.length == 1 && reuse.getOffset() == 0),
                 "Reuse BinaryRecordData should have no segments or only one segment and offset start at 0.");
 
-        int arity = source.readInt();
         int length = source.readInt();
         if (segments == null || segments[0].size() < length) {
             segments = new MemorySegment[] {MemorySegmentFactory.wrap(new byte[length])};