Missing unregisterCompositorLogic

[dark_sylinc]

I just noticed CompositorManager::registerCompositorLogic() doesn't have it's corresponding unregisterCompositorLogic()

I saw Deferred Shading demo which is the only one who uses it and there's clearly a memory leak.
There is no smart ptr so it isn't tracked through ref. counting.

I don't think smart ptrs should be used though, since listeners may derive from user-created classes that may be completely independent from Ogre (except from the bit they derive from Ogre::CompositorLogic)

If anyone doesn't object, I'm going add the corresponding unregister() very soon

[dark_sylinc]

Fix checked in.

I've noticed there's also no CompositorManager::unregisterCustomCompositionPass() but I haven't dealt with it yet