Fix redundant management of libvlc instances in VLCLibrary

This is more like a question than MR, but...

VLCLibrary stores libvlc_new() internally when creating an instance and uses libvlc_release() in VLCLibrary.dealloc, so isn't it unnecessary to manage it outside the VLCLibrary instance?

I apologize if there was any intention or if I was fundamentally wrong.

best regards.