Remove the JPDA demo

demo/jpda is legacy crud from the original JPDA development.

This bug requests that this demo be dropped and the code in com.sun.tools.example.trace and com.sun.tools.example.debug.{gui,bdi,event} be deleted.

The motive for this request is the restructure of the source code by module. The example/demo JPDA code does not fit well into the new structure because the source code is used for both jdb and for the demo. As the demo is legacy then we should just drop it (it's incomplete and not very useful anyway).