Appease the gods in introspection

Reduce the amount of bogus warnings g-ir-scanner prints out.

clutter/clutter-snap-constraint.c

@@ -53,8 +53,6 @@
 #define CLUTTER_IS_SNAP_CONSTRAINT_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), CLUTTER_TYPE_SNAP_CONSTRAINT))
 #define CLUTTER_SNAP_CONSTRAINT_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), CLUTTER_TYPE_SNAP_CONSTRAINT, ClutterSnapConstraintClass))
 
-typedef struct _ClutterSnapConstraintClass      ClutterSnapConstraintClass;
-
 struct _ClutterSnapConstraint
 {
   ClutterConstraint parent_instance;