HDFS-15017. Remove redundant import of AtomicBoolean in NameNodeConnector. Contributed by Chao Sun.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/balancer/NameNodeConnector.java

@@ -28,7 +28,6 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
 
 import org.apache.commons.logging.Log;