Issue #21 - Remove use counters telemetry

This reverts Bug 968923 - Implement some equivalent of Chrome's use counters (on top of telemetry?)

For reference: https://bugzilla.mozilla.org/show_bug.cgi?id=968923

image/DynamicImage.cpp

@@ -337,11 +337,5 @@ DynamicImage::Unwrap()
   return self.forget();
 }
 
-void
-DynamicImage::PropagateUseCounters(nsIDocument*)
-{
-  // No use counters.
-}
-
 } // namespace image
 } // namespace mozilla