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/samplecode/SampleLighting.cpp b/samplecode/SampleLighting.cpp
index bab2b5d..2218f31 100755
--- a/samplecode/SampleLighting.cpp
+++ b/samplecode/SampleLighting.cpp
@@ -22,7 +22,7 @@
     SkLights::Builder builder;
 
     builder.add(SkLights::Light::MakeDirectional(SkColor3f::Make(1.0f, 1.0f, blue), dir));
-    builder.add(SkLights::Light::MakeAmbient(SkColor3f::Make(0.1f, 0.1f, 0.1f)));
+    builder.setAmbientLightColor(SkColor3f::Make(0.1f, 0.1f, 0.1f));
 
     return builder.finish();
 }