Remove cookie alpha channel support

ScriptableRenderPipeline/HDRenderPipeline/Lighting/LightLoop/LightLoopDef.hlsl

 // ----------------------------------------------------------------------------
 
 // Used by directional and spot lights.
-// Returns the color in the RGB components, and the transparency (lack of occlusion) in A.
-float4 SampleCookie2D(LightLoopContext lightLoopContext, float2 coord, int index)
+float3 SampleCookie2D(LightLoopContext lightLoopContext, float2 coord, int index)
-    return SAMPLE_TEXTURE2D_ARRAY_LOD(_CookieTextures, sampler_CookieTextures, coord, index, 0);
+    return SAMPLE_TEXTURE2D_ARRAY_LOD(_CookieTextures, sampler_CookieTextures, coord, index, 0).rgb;
-// Returns the color in the RGB components, and the transparency (lack of occlusion) in A.
-float4 SampleCookieCube(LightLoopContext lightLoopContext, float3 coord, int index)
+float3 SampleCookieCube(LightLoopContext lightLoopContext, float3 coord, int index)
-    return SAMPLE_TEXTURECUBE_ARRAY_LOD_ABSTRACT(_CookieCubeTextures, sampler_CookieCubeTextures, coord, index, 0);
+    return SAMPLE_TEXTURECUBE_ARRAY_LOD_ABSTRACT(_CookieCubeTextures, sampler_CookieCubeTextures, coord, index, 0).rgb;
 }
 
 //-----------------------------------------------------------------------------

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.hlsl

 // EvaluateBSDF_Directional
 //-----------------------------------------------------------------------------
 
-float4 EvaluateCookie_Directional(LightLoopContext lightLoopContext, DirectionalLightData lightData,
+float3 EvaluateCookie_Directional(LightLoopContext lightLoopContext, DirectionalLightData lightData,
                                   float3 lighToSample)
 {
     // Compute the CS position (in [-1, 1]^2) by projecting 'positionWS' onto the near plane.
     positionNDC = lightData.tileCookie ? frac(positionNDC) : positionNDC;
 
     // We let the sampler handle clamping to border.
-    float4 cookie = SampleCookie2D(lightLoopContext, positionNDC, lightData.cookieIndex);
-
-    return cookie;
+    return SampleCookie2D(lightLoopContext, positionNDC, lightData.cookieIndex);
 }
 
 // None of the outputs are premultiplied.
     [branch] if (lightData.cookieIndex >= 0)
     {
         float3 lightToSample = positionWS - lightData.positionWS;
-        float4 cookie = EvaluateCookie_Directional(lightLoopContext, lightData, lightToSample);
+        float3 cookie = EvaluateCookie_Directional(lightLoopContext, lightData, lightToSample);
-        color       *= cookie.rgb;
-        attenuation *= cookie.a;
+        color *= cookie;
     }
 }
 
 
     [branch] if (lightType == GPULIGHTTYPE_POINT)
     {
-        cookie = SampleCookieCube(lightLoopContext, positionLS, lightData.cookieIndex);
+        cookie.rgb = SampleCookieCube(lightLoopContext, positionLS, lightData.cookieIndex);
+        cookie.a   = 1;
     }
     else
     {
         float2 positionNDC = positionCS * 0.5 + 0.5;
 
         // Manually clamp to border (black).
-        cookie = SampleCookie2D(lightLoopContext, positionNDC, lightData.cookieIndex);
-        cookie.a = isInBounds ? cookie.a : 0;
+        cookie.rgb = SampleCookie2D(lightLoopContext, positionNDC, lightData.cookieIndex);
+        cookie.a   = isInBounds ? 1 : 0;
     }
 
     return cookie;