VEraseOverlayPoints - erases 1-bit overlay points.
  VEraseOverlayPoints(win, ovl, points, npoints)
  Window win;
  int ovl;
  XPoint *points;
  int npoints;
  VEraseOverlayPoints erases 1-bit overlay points (pixels), in the image 
window or one of its subwindows. 
Return Value
  0 - work successfully.
  1 - memory allocation error.
  6 - invalid window ID.
  225 - no overlay created.
  237 - the overlay is not on.
  win - the image window ID or one of its subwindows' ID.
  ovl - specifies the overlay number to be used to erase the points.
  points - specifies a pointer to an array of XPoint structures containing
        the positions of the points.
  npoints - specifies the number of points to be erased.
Side Effects
Entry Conditions
  If ovl or npoint is not valid, or points is NULL, or VCreateColormap is
not called earlier, VEraseOverlayPoints prints an error message to the
standard error stream, produces a core dump file and exits from the current
Related Functions
VDisplayOverlayPoints, VEraseOverlay. VTurnOffOverlay.