compositor: Remove desktop zoom

Zoom is a neat trick, but in its current form it's very hard to test
and maintain.

It also causes output damage to scale outside of the output's boundaries,
which leads to an extra clipping step that's only necessary when zoom
is enabled.

Remove it to simplify desktop-shell and compositor.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

include/libweston/libweston.h

@@ -150,21 +150,6 @@ struct weston_spring {
 	uint32_t clip;
 };
 
-struct weston_output_zoom {
-	bool active;
-	float increment;
-	float level;
-	float max_level;
-	float trans_x, trans_y;
-	struct {
-		double x, y;
-	} current;
-	struct weston_seat *seat;
-	struct weston_animation animation_z;
-	struct weston_spring spring_z;
-	struct wl_listener motion_listener;
-};
-
 /* bit compatible with drm definitions. */
 enum dpms_enum {
 	WESTON_DPMS_ON,
@@ -324,7 +309,6 @@ struct weston_output {
 	/** For cancelling the idle_repaint callback on output destruction. */
 	struct wl_event_source *idle_repaint_source;
 
-	struct weston_output_zoom zoom;
 	int dirty;
 	struct wl_signal frame_signal;
 	struct wl_signal destroy_signal;	/**< sent when disabled */
@@ -1876,11 +1860,6 @@ void
 weston_compositor_exit_with_code(struct weston_compositor *compositor,
 				 int exit_code);
 void
-weston_output_update_zoom(struct weston_output *output);
-void
-weston_output_activate_zoom(struct weston_output *output,
-			    struct weston_seat *seat);
-void
 weston_output_add_destroy_listener(struct weston_output *output,
 				   struct wl_listener *listener);
 struct wl_listener *