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/shadowmaps.cpp b/gm/shadowmaps.cpp
index 6c9738b..d8682ce 100644
--- a/gm/shadowmaps.cpp
+++ b/gm/shadowmaps.cpp
@@ -74,7 +74,7 @@
                                                      SkVector3::Make(0.2f, 0.1f, 1.0f)));
         builder.add(SkLights::Light::MakeDirectional(SkColor3f::Make(0.4f, 0.3f, 0.2f),
                                                      SkVector3::Make(0.1f, 0.2f, 1.0f)));
-        builder.add(SkLights::Light::MakeAmbient(SkColor3f::Make(0.4f, 0.4f, 0.4f)));
+        builder.setAmbientLightColor(SkColor3f::Make(0.4f, 0.4f, 0.4f));
         fLights = builder.finish();
 
         fShadowParams.fShadowRadius = 4.0f;