HADOOP-15404. Remove multibyte characters in DataNodeUsageReportUtil

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>

hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/server/protocol/DataNodeUsageReportUtil.java

@@ -23,7 +23,7 @@ import org.apache.hadoop.util.Time;
 
 /**
  * This class is helper class to generate a live usage report by calculating
- * the delta between  current DataNode usage metrics and the usage metrics
+ * the delta between current DataNode usage metrics and the usage metrics
  * captured at the time of the last report.
  */
 @InterfaceAudience.Private