Revert "HADOOP-14948. Document missing config key hadoop.treat.subject.external. Contributed by Ajay Kumar."

This reverts commit 1452ba139ea845ad9e82a5902d239b59a789bff3.

hadoop-common-project/hadoop-common/src/main/resources/core-default.xml

@@ -2918,17 +2918,4 @@
     </description>
     <name>hadoop.zk.auth</name>
   </property>
-  <property>
-    <name>hadoop.treat.subject.external</name>
-    <value>false</value>
-    <description>
-      When creating UGI with UserGroupInformation(Subject), treat the passed
-      subject external if set to true, and assume the owner of the subject
-      should do the credential renewal.
-
-      When true this property will introduce an incompatible change which
-      may require changes in client code. For more details, see the jiras:
-      HADOOP-13805,HADOOP-13558.
-    </description>
-  </property>
 </configuration>