RFR: JDK-8203946: Move UnpackSecurity.gmk to closed

[Tim Bell]

Erik:

> The UnpackSecurity.gmk build logic has never belonged in OpenJDK and
> should be moved to Oracle's internal makefiles.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8203946
>
> Webrev: http://cr.openjdk.java.net/~erikj/8203946/webrev.01/

Looks good.

/Tim