Remove experimental, non-shipping glass SWT platform

In the graphics module we have an experimental implementation of an SWT-based platform. This was never a good place for it, since we do not want jfxrt.jar (even in debug mode) to have to depend on swt.jar. With the modular JDK there is no way for this to be supported. We need to remove this experimental code. If someone wants to resurrect it, it will need to be in a separate (also experimental and not shipped) module.