YARN-11226. Fix CheckStyle.

Author: slfan1989

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-router/src/test/java/org/apache/hadoop/yarn/server/router/webapp/MockDefaultRequestInterceptorREST.java

@@ -78,7 +78,6 @@
 import org.apache.hadoop.yarn.server.resourcemanager.MockRM;
 import org.apache.hadoop.yarn.server.resourcemanager.RMContext;
 import org.apache.hadoop.yarn.server.resourcemanager.reservation.ReservationSystem;
-import org.apache.hadoop.yarn.server.resourcemanager.reservation.ReservationSystemTestUtil;
 import org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMApp;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.ActiveUsersManager;
 import org.apache.hadoop.yarn.server.resourcemanager.scheduler.ResourceScheduler;