HOTFIX: remove unused import to fix checkstyle error

Author: mjsax

clients/src/test/java/org/apache/kafka/common/serialization/SerializationTest.java

@@ -33,7 +33,6 @@
 import java.util.LinkedList;
 import java.util.Stack;
 
-import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.apache.kafka.common.utils.Utils.wrapNullable;
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;