HDFS-16756: Fixup for 3.3 backport.

hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/router/RouterRpcClient.java

@@ -23,7 +23,6 @@ import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.HADOOP_CALLER_C
 import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.IPC_CLIENT_CONNECT_MAX_RETRIES_ON_SOCKET_TIMEOUTS_KEY;
 import static org.apache.hadoop.fs.CommonConfigurationKeysPublic.IPC_CLIENT_CONNECT_TIMEOUT_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_IP_PROXY_USERS;
-import static org.apache.hadoop.hdfs.server.federation.fairness.RouterRpcFairnessConstants.CONCURRENT_NS;
 
 import java.io.EOFException;
 import java.io.FileNotFoundException;