Remove external BitmapImage lazy decoding tracking

Source/platform/graphics/BitmapImage.h

Index: Source/platform/graphics/BitmapImage.h
diff --git a/Source/platform/graphics/BitmapImage.h b/Source/platform/graphics/BitmapImage.h
index 26ba1279d6eb9b8ee5a19ab06c3cc0c5e87013cb..821c78b3d2ebf14908983706674a5932b89aad46 100644
--- a/Source/platform/graphics/BitmapImage.h
+++ b/Source/platform/graphics/BitmapImage.h
@@ -118,7 +118,6 @@ private:
     float frameDurationAtIndex(size_t);
     bool frameHasAlphaAtIndex(size_t);
     ImageOrientation frameOrientationAtIndex(size_t);
-    bool frameIsLazyDecodedAtIndex(size_t) const;
 
     // Decodes and caches a frame. Never accessed except internally.
     void cacheFrame(size_t index);