Remove x11vnc subdir.

The new x11vnc repo is at https://github.com/LibVNC/x11vnc.
Remove tightvnc-1.3dev5-vncviewer-alpha-cursor.patch.
Remove x11vnc from autotools build system.
Move prepare_x11vnc_dist.sh over to x11vnc repo.
Move VisualNaCro to https://github.com/LibVNC/VisualNaCro.
Move vncterm to https://github.com/LibVNC/vncterm.
The HAVE_X11 define is not there anymore, but we don't need it either.