Moved ambient lights out of SkLight's light array

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2287553002

Committed: https://skia.googlesource.com/skia/+/8f98f0aa2d3f7571a890b916c7c4b5ee831e9686
Review-Url: https://codereview.chromium.org/2287553002
diff --git a/gm/lightingshader.cpp b/gm/lightingshader.cpp
index 4a79ebe..137fd64 100644
--- a/gm/lightingshader.cpp
+++ b/gm/lightingshader.cpp
@@ -52,7 +52,7 @@
                                                      SkVector3::Make(SK_ScalarRoot2Over2,
                                                                      0.0f,
                                                                      SK_ScalarRoot2Over2)));
-        builder.add(SkLights::Light::MakeAmbient(SkColor3f::Make(0.2f, 0.2f, 0.2f)));
+        builder.setAmbientLightColor(SkColor3f::Make(0.2f, 0.2f, 0.2f));
 
         fLights = builder.finish();
     }