RFR JDK-8163145: remove two null lines in the end of message.properties

[Leo Jiang]

Hi all,

Please help to review the change for this minor bug. Two lines with text 'null' is in the end of message.properties, 
which are non-functional.

webrev:
http://cr.openjdk.java.net/~fyuan/leo/8163145/

bug:
https://bugs.openjdk.java.net/browse/JDK-8163145

Thanks,
Leo