Revert "HDFS-7383. Merged to branch-2.6 also."

This reverts commit 755af2768b2be1ded532e795db30ec0bfea03e66.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -1273,9 +1273,6 @@ Release 2.6.0 - UNRELEASED
     HDFS-7382. DataNode in secure mode may throw NullPointerException if client
     connects before DataNode registers itself with NameNode. (cnauroth)
 
-    HDFS-7383. DataNode.requestShortCircuitFdsForRead may throw 
-    NullPointerException. (szetszwo via suresh)
-
 Release 2.5.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES