Clean up glTF models used in tests

As part of the Model.js refactor effor the [Specs/Data/Models](https://github.com/CesiumGS/cesium/tree/master/Specs/Data/Models) could use some cleanup

* Many of the sample models are glTF 1.0 but they don't need to be
* Texture files are larger than necessary in some cases
* CRN and KTX1 texture support will be deprecated soon and those models should be removed
* A new folder was added in https://github.com/CesiumGS/cesium/pull/9505 that has some duplicates with the parent folder. These should be unified. See https://github.com/CesiumGS/cesium/pull/9505#discussion_r619230522 for discussion