HDFS-16647. Delete unused NameNode#FS_HDFS_IMPL_KEY. (#4525). Contributed by JiangHua Zhu.

Signed-off-by: Ayush Saxena <ayushsaxena@apache.org>

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/NameNode.java

@@ -403,7 +403,6 @@ public class NameNode extends ReconfigurableBase implements
    */
   @Deprecated
   public static final int DEFAULT_PORT = DFS_NAMENODE_RPC_PORT_DEFAULT;
-  public static final String FS_HDFS_IMPL_KEY = "fs.hdfs.impl";
   public static final Logger LOG =
       LoggerFactory.getLogger(NameNode.class.getName());
   public static final Logger stateChangeLog =