Avoid netscape.javascript.JSObject in nashorn code

nashorn uses it's own copy of netscape.javascript.JSObject class. It should avoid getWindow(Applet) in it - which anyway throws unsupported exception - but brings in compile time dependency on Applet class.

It is better if nashorn renames it's JSObject to be jdk.nashorn.api.scripting.JSObject and avoid getWindow(Applet) method in it. The later is useful for non-desktop profiles as well.