Revert "Experimental HDR procedural sky"
Revert "Experimental HDR procedural sky"

This reverts commit ec89263240474e1546564bae529d605481a3db9e.

AnalyticalGraphicsInc/cesium,YonatanKra/cesium,soceur/cesium,geoscan/cesium,soceur/cesium,soceur/cesium,CesiumGS/cesium,likangning93/cesium,YonatanKra/cesium,likangning93/cesium,josh-bernstein/cesium,progsung/cesium,geoscan/cesium,kaktus40/cesium,hodbauer/cesium,CesiumGS/cesium,josh-bernstein/cesium,kaktus40/cesium,CesiumGS/cesium,jasonbeverage/cesium,CesiumGS/cesium,progsung/cesium,hodbauer/cesium,YonatanKra/cesium,likangning93/cesium,jasonbeverage/cesium,likangning93/cesium,likangning93/cesium,CesiumGS/cesium,AnalyticalGraphicsInc/cesium,hodbauer/cesium,YonatanKra/cesium