Remove the workaround for the PSSL compiler bug (it's been fixed)

Assets/ScriptableRenderPipeline/ShaderLibrary/AreaLighting.hlsl

             float a = cosOmega * acos(x) - z;                       // y*ArcCos[-y*Sqrt[(1/x-1)/(1-y^2)]]-Sqrt[(1-y^2)*(x/(1-x))-y^2]*(1/x-1)
             float b = atan(y);                                      // ArcTan[Sqrt[(1-y^2)*(x/(1-x))-y^2]]
 
-            // Replacing max() with saturate() results in a 12 cycle SGPR forwarding stall on PS4.
-            return max(INV_PI * (a * sinSqSigma + b), 0);           // (a/Pi)*x+(b/Pi)
+            return saturate(INV_PI * (a * sinSqSigma + b));
         }
     #endif
 #endif