Bug 1167356 - Remove no-longer needed assertion.

CLOSED TREE

image/RasterImage.cpp

@@ -691,7 +691,6 @@ RasterImage::CopyFrame(uint32_t aWhichFrame, uint32_t aFlags)
     return nullptr;
   }
 
-  NS_ASSERTION(success, "Failed to map surface");
   RefPtr<DrawTarget> target =
     Factory::CreateDrawTargetForData(BackendType::CAIRO,
                                      mapping.mData,