Update CHANGES.txt to move MAPREDUCE-6436 from YARN to MAPREDUCE

(cherry picked from commit 7092d47fc0b3b792dd31f967c01d460dc089f60b)

Conflicts:
	hadoop-mapreduce-project/CHANGES.txt
	hadoop-yarn-project/CHANGES.txt

hadoop-mapreduce-project/CHANGES.txt

@@ -8,6 +8,8 @@ Release 2.7.3 - UNRELEASED
 
   IMPROVEMENTS
 
+    MAPREDUCE-6436. JobHistory cache issue. (Kai Sasaki via zxu)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-yarn-project/CHANGES.txt

@@ -48,8 +48,6 @@ Release 2.7.3 - UNRELEASED
 
     YARN-4439. Clarify NMContainerStatus#toString method. (Jian He via xgong)
 
-    MAPREDUCE-6436. JobHistory cache issue. (Kai Sasaki via zxu)
-
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES