Clean up the SkyHDRI shader

Assets/ScriptableRenderLoop/HDRenderLoop/Sky/Resources/SkyHDRI.shader

             #pragma vertex Vert
             #pragma fragment Frag
 
-            #pragma multi_compile _ ATMOSPHERICS_DEBUG
-            #pragma multi_compile _ ATMOSPHERICS_OCCLUSION_FULLSKY
-            #pragma multi_compile _ PERFORM_SKY_OCCLUSION_TEST
-
-            #ifndef PERFORM_SKY_OCCLUSION_TEST
-                #define IS_RENDERING_SKY
-            #endif
-
-            #include "Assets/ScriptableRenderLoop/HDRenderLoop/ShaderVariables.hlsl"
 
             TEXTURECUBE(_Cubemap);
             SAMPLERCUBE(sampler_Cubemap);