ui/gfx: Remove the deprecated "operator const GdkPixbuf*" from Image API.

ui/gfx/image/image.cc

Index: ui/gfx/image/image.cc
diff --git a/ui/gfx/image/image.cc b/ui/gfx/image/image.cc
index 717ea941a0908acfbeb3c8c642b3f1b3678d0d26..092047f14e1b1a91266a3ec94afe724bd84ca80a 100644
--- a/ui/gfx/image/image.cc
+++ b/ui/gfx/image/image.cc
@@ -330,12 +330,6 @@ Image::operator const SkBitmap&() const {
   return *ToSkBitmap();
 }
 
-#if defined(TOOLKIT_USES_GTK)
-Image::operator GdkPixbuf*() const {
-  return ToGdkPixbuf();
-}
-#endif
-
 #if defined(OS_MACOSX)
 Image::operator NSImage*() const {
   return ToNSImage();