Hi there,
approximateTerrainHeights.json is used to estimate terrain heights when clamping geometry to the ground. If you are not using that option, you should be fine to omit that file.
The IAU2006_XYS files are used when converting between the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF), which is mostly used for objects in orbit, so if you are not doing that you may omit those files as well.
Thanks,
Gabby