glutRemoveOverlay - removes the overlay (if one exists) from the current window.
void glutRemoveOverlay(void);
glutRemoveOverlay removes the overlay (if one exists). It is safe to call
glutRemoveOverlay even if no overlay is currently established--it does nothing
in this case. Implicitly, the window's layer in use changes to the normal
plane immediately once the overlay is removed.
If the program intends to re-establish the overlay later, it is
typically faster and less resource intensive to use glutHideOverlay and
glutShowOverlay to simply change the display status of the overlay.
glutEstablishOverlay, glutDestroyWindow
Mark J. Kilgard (mjk@nvidia.com)