Remove full support for colour maps

Gets rid of a loooot of code and complexity.

Colour map clients are still supported through an
automatically generated map, but we lose the ability to
develop a client or server that uses colour maps
internally.
diff --git a/unix/x0vncserver/XPixelBuffer.h b/unix/x0vncserver/XPixelBuffer.h
index 29ae94a..ab4f88e 100644
--- a/unix/x0vncserver/XPixelBuffer.h
+++ b/unix/x0vncserver/XPixelBuffer.h
@@ -37,8 +37,7 @@
 class XPixelBuffer : public FullFramePixelBuffer
 {
 public:
-  XPixelBuffer(Display *dpy, ImageFactory &factory,
-               const Rect &rect, ColourMap* cm);
+  XPixelBuffer(Display *dpy, ImageFactory &factory, const Rect &rect);
   virtual ~XPixelBuffer();
 
   // Provide access to the underlying Image object.