HDFS-16294.Remove invalid DataNode#CONFIG_PROPERTY_SIMULATED. (#3605)

(cherry picked from commit 72718a8dc1d6d16249c1073c31f1a078d4e118f6)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java

@@ -1360,7 +1360,7 @@ public class DataNode extends ReconfigurableBase
   /**
    * This method starts the data node with the specified conf.
    * 
-   * If conf's CONFIG_PROPERTY_SIMULATED property is set
+   * If conf's DFS_DATANODE_FSDATASET_FACTORY_KEY property is set
    * then a simulated storage based data node is created.
    * 
    * @param dataDirectories - only for a non-simulated storage data node