Make some types private

Removed the following from the Cesium API: `Transforms.earthOrientationParameters`, `EarthOrientationParameters`, `EarthOrientationParametersSample`, `Transforms.iau2006XysData`, `Iau2006XysData`, `Iau2006XysSample`, `IauOrientationAxes`, `TimeConstants`, `Scene.frameState`, `FrameState`, `EncodedCartesian3`, `EllipsoidalOccluder`, and `FAR`.  These are still available but are not part of the official API and may change in future versions.

Part of #1688.