Apply UsdSkel without relying on UsdSkelBakeSkinning in the procedural

[sebastienblor]

Currently, in the procedural we call UsdSkelBakeSkinning in order to apply the UsdSkel skinning in the whole scene. But this usd API doesn't seem to be very widely used, and we keep getting usd errors in crowd scenes generated by Houdini. We shouldn't rely on this API anymore and instead replicate what's being done in hydra for each UsdSkel primitive