YARN-11515. Fix CheckStyle.

Author: slfan1989

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/main/java/org/apache/hadoop/yarn/server/router/clientrm/DefaultClientRequestInterceptor.java

@@ -22,7 +22,6 @@
 import java.security.PrivilegedExceptionAction;
 
 import org.apache.hadoop.conf.Configuration;
-import org.apache.hadoop.util.StringUtils;
 import org.apache.hadoop.yarn.api.ApplicationClientProtocol;
 import org.apache.hadoop.yarn.api.protocolrecords.CancelDelegationTokenRequest;
 import org.apache.hadoop.yarn.api.protocolrecords.CancelDelegationTokenResponse;