This interface was used by Boxes.moov. This CL removes the interface and just uses the Track object directly.
Since Track is package-private it seems fine to use it directly.
The drawback with interface is that, with every new field addition in the
Track class, we need to update the interface as well (if we need to access that field for moov box).
PiperOrigin-RevId: 669295399
791483f2d3