function unbindGamepad(index, button) {
	if (!bindings[index]) {
		throw new Error("no bindings for gamepad " + index);
	}
	bindings[index].buttons[button] = {};
}
unbind the defined keycode
@param {number} index - Gamepad index
@param {number} button - (See {@link input.GAMEPAD})
@example
me.input.unbindGamepad(0, me.input.GAMEPAD.BUTTONS.FACE_1);