RFR(S): 8211350: Remove jprt support

[Mandy Chung]

On 10/2/18 12:21 AM, Mikael Vidstedt wrote:
> Please review this change which removes support for, and references to, the (Oracle internal) JPRT system.
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8211350
> webrev: http://cr.openjdk.java.net/~mikael/webrevs/8211350/webrev.00/open/webrev/
>

test/jdk/tools/lib/tests/Helper.java is used by test/jdk/tools/jimage 
and test/jdk/tools/jlink tests which will be skipped, rather than 
failing, when running with images where jmods directory is not present 
(e.g. exploded image).

I think Helper class should continue to return null if jmods does not 
exist.  test/jdk/tools/jimage/JImageTest.java should also be reverted.

Otherwise, the clean up looks good.

Mandy