RFR: 8075277 : JDK is still building X11 related Java files on OSX

[Phil Race]

Bug: https://bugs.openjdk.java.net/browse/JDK-8075277
Fix: http://cr.openjdk.java.net/~prr/8075277/

Although a more complete fix would do something like refactor the source 
files,
as that would be less fragile amongst other things, this at least gets 
us into a
better shape with minimal disruption - and solves my immediate problem :-)

However, it was not sufficient to modify the build file since NativeFont
needs to have an implementation and the unix (aka X11) one just drags
in everything else. So I have a stub version, the same as on Windows.

And it is not clear to me why there was an unused reference to
FontConfigManager in the Mac code. Removing it breaks
a link that dragged in X11 related code.

I expect the files shipped on OS X to go down as a result of
removing these 'dead' ones.
I would also have got rid of the Windows L&F but that needs
a bit of work on the Swing side first : 
https://bugs.openjdk.java.net/browse/JDK-8075255

-phil.