script: Let ClutterActor parse behaviours

Up until now, the "behaviours" member of an actor definition was parsed
by the ClutterScript parser itself - even though it's not strictly
necessary.

In an effort to minimize the ad hoc code in the Script parser, we should
let ClutterActor handle all the special cases that involve
actor-specific members.

clutter/clutter-script-private.h

@@ -58,7 +58,6 @@ typedef struct {
 
   GList *properties;
   GList *children;
-  GList *behaviours;
   GList *signals;
 
   GType gtype;