[9] Review Request: 6368321 MetalRootPaneUI calls to deprecated code

[Sergey Bylokhov]

Hello.
Please review the fix for jdk9. I do not plan to backport it to jdk8.
Usage of deprecated methods(xxxMenuBar()) were removed as suggested in 
the bug comments.
The fix is a part of https://bugs.openjdk.java.net/browse/JDK-8066622 
efforts.

Bug: https://bugs.openjdk.java.net/browse/JDK-6368321
Webrev can be found at: http://cr.openjdk.java.net/~serb/6368321/webrev.00

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Best regards, Sergey.