Deselects the selected cell or cells.
If the selection mode is
NSRadioModeMatrix and empty selection is not allowed, or if nothing is currently selected, this method does nothing. This method doesn’t redisplay the receiver.
Selecting and Deselecting Cells
Selects and highlights all cells in the receiver.
The cell that will be clicked when the user presses the Space bar.
Deselects all cells in the receiver and, if necessary, redisplays the receiver.