Remove uses of SkImageDecoder from samplecode

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1812323003

Review URL: https://codereview.chromium.org/1812323003
diff --git a/samplecode/SampleLayers.cpp b/samplecode/SampleLayers.cpp
index 1183568..b31c839 100644
--- a/samplecode/SampleLayers.cpp
+++ b/samplecode/SampleLayers.cpp
@@ -14,7 +14,7 @@
 #include "SkColorPriv.h"
 #include "SkDevice.h"
 #include "SkGradientShader.h"
-#include "SkImageDecoder.h"
+#include "SkImage.h"
 #include "SkInterpolator.h"
 #include "SkMaskFilter.h"
 #include "SkPath.h"