fix checkstyle

Author: hfutatzhanghb

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/TestDFSOutputStream.java

@@ -32,7 +32,6 @@
 import java.util.Random;
 import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicBoolean;
-import java.util.zip.Checksum;
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.CreateFlag;