[server] Don't set a parent on BufferInterface
BufferInterface used to have a SurfaceInterface as parent. This could result in easily hitting the abort condition that the BufferInterface was still referenced when it gets deleted by just having one other user referencing the BufferInterface. There is no need to have the BufferInterface deleted when the SurfaceInterface to which it belongs gets deleted. The BufferInterface will get deleted once it's completely unreferenced and also has a destroy listener.