possible memory leak

change the event that will be dispatched when emission of particles is finished from "COMPLETE" to "REMOVE_FROM_JUGGLER".

if someone wrote
<code>Starling.juggler.add(mParticleSystem);</code>
but didn't remove manually like this
<code>Starling.juggler.remove(mParticleSystem);</code>
that will cause memory leak.

and other objects that can be added to juggler are not require remove manually.