compositor.h: Remove unused variable from weston_seat structure

This variable may have been used previously when evdev.c was used
however that functionality seems to have been consumed by libinput, so
there is no need for this variable in the weston_seat structure anymore.

Signed-off-by: Chris Michael <cp.michael@samsung.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>

src/compositor.h

@@ -561,7 +561,6 @@ struct weston_seat {
 
 	void (*led_update)(struct weston_seat *ws, enum weston_led leds);
 
-	uint32_t slot_map;
 	struct input_method *input_method;
 	char *seat_name;
 };