delete a load of unused animation time control code

Models and animations need some reworking anyway to separate per-model data
(meshes, materials, animation hierarchy, keyframes) from per-instance data
(pattern/decal/label/effect state, animation state, cached transforms).
Reworking stuff is usually easier when there's less stuff to rework, so
therefore deleting stuff is good (right?)
Remove looping capability from Animation::Interpolate()
Change scale & position animation too