Updating all CHANGES.txt files to move entires from future releases into 2.6.1

section given the large number of backports to 2.6.1. Contd..

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -492,9 +492,6 @@ Release 2.8.0 - UNRELEASED
     HADOOP-12076. Incomplete Cache Mechanism in CredentialProvider API.
     (Larry McCay via cnauroth) 
 
-    HADOOP-8151. Error handling in snappy decompressor throws invalid
-    exceptions. (Matt Foley via harsh)
-
     HADOOP-12119. hadoop fs -expunge does not work for federated namespace
     (J.Andreina via vinayakumarb)