VDeleteButton - removes a Button Item from the list.
  VDeleteButton removes the Button Item from the list and erases the button
from the window it is diaplyed in. The memory space occupied by the Button 
Item is also freed. Please note that VDeleteButton should not be used for a
panel button (see VErasePanel).
  typedef struct _button {
        Window  win;            /*window in which item resides*/
        short   type;           /*type of button(0=button, 1=toggle, etc..)*/
        short   x,y;            /*location of upper-left corner of item*/
        short   w;              /*width of the item area in fonts*/
        short   h;              /*height of the item area in fonts*/
        short   label_width;    /*width of label in pixels*/
        short   label_height;   /*height of label*/
        short   label_ascent;   /*ascent dimension of font*/
        short   label_x;        /*position of the label*/
        short   label_y;
        short   thick;          /*thickness of frame*/
        short   width;          /*width of item in pixels*/
        short   height;         /*height of item in pixels*/
        int     fw,fh;          /*size of font*/
        char    label[150];     /*label of the button item*/
        short   state;          /*indicates if button item is OFF(0) / ON(1)*/
        short   mode;           /*0=RELEASED, 1=PRESSED*/
        int     (*func)();      /*notify procedure*/
        struct _button *next;   /*next button item*/
Return Value
  0 - work successfully.
  266 - invalid Button Item ID.
  ID - the ID of the Button Item  to be deleted.
Side Effects
  An entry is removed from the Button Item list. The region occupied by the
Item is erased.
Entry Conditions
  VCreateColormap should be called earlier, else VDeleteButton prints an
error message to the standard error stream, produces a core dump file and
exits from the current process.
Related Functions
VAddButton, VClearButtonList, VSetButtonOff.