Use IOSImageDataFetcherWrapper for favicon

ios/web/public/test/fakes/test_web_state.mm

Index: ios/web/public/test/fakes/test_web_state.mm
diff --git a/ios/web/public/test/fakes/test_web_state.mm b/ios/web/public/test/fakes/test_web_state.mm
index 9b821db7b55bd45911a48942852be86b2bdc9fd9..5864167a41024d6ffcfd32672d8f79138da9bb47 100644
--- a/ios/web/public/test/fakes/test_web_state.mm
+++ b/ios/web/public/test/fakes/test_web_state.mm
@@ -183,14 +183,6 @@ CRWWebViewProxyType TestWebState::GetWebViewProxy() const {
   return nullptr;
 }
 
-int TestWebState::DownloadImage(const GURL& url,
-                                bool is_favicon,
-                                uint32_t max_bitmap_size,
-                                bool bypass_cache,
-                                const ImageDownloadCallback& callback) {
-  return 0;
-}
-
 service_manager::InterfaceRegistry* TestWebState::GetMojoInterfaceRegistry() {
   return nullptr;
 }