Remove the VNC client and server

The VNC server and client was a really cool feature back in 2002/2003 when it was implemented. The Contiki VNC server allowed an embedded Contiki device to produce a graphical user interface over the Internet. The Contiki VNC client allowed a display-equipped Contiki device to remotely access a graphical user interface over the Internet. Screenshot of the VNC server running on an AVR below.

![contiki-avr](https://f.cloud.github.com/assets/589970/1626879/860f295e-56e8-11e3-9508-a6a4315439c3.png)

But the VNC feature isn't used much any more (not sure if it even is compatible with today's VNC viewers) and it is time to remove it.