Remove usage of unstable box syntax, except in the script crate

… because there’s a lot of it,
and script still uses any other unstable features anyway.

components/devtools/actors/object.rs

@@ -34,7 +34,7 @@ impl ObjectActor {
             };
 
             registry.register_script_actor(uuid, name.clone());
-            registry.register_later(box actor);
+            registry.register_later(Box::new(actor));
 
             name
         } else {