remove typedef `Decoration`

dwl.c

@@ -119,11 +119,6 @@ typedef struct {
 	int isfullscreen;
 } Client;
 
-typedef struct {
-	struct wl_listener request_mode;
-	struct wl_listener destroy;
-} Decoration;
-
 typedef struct {
 	uint32_t mod;
 	xkb_keysym_t keysym;