Remove the case which acos() does not support

Assets/ScriptableRenderPipeline/ShaderLibrary/AreaLighting.hlsl

     float omega = acos(cosOmega);
     float gamma = asin(sinGamma);
 
-    if (omega < 0 || omega >= HALF_PI + sigma)
+    if (omega >= HALF_PI + sigma)
     {
         // Full horizon occlusion (case #4).
         return 0;