dialog: Remove icons from dialogs

According to the new mockups, remove the icon from MessageDialogContent

See https://gitlab.gnome.org/GNOME/gnome-shell/issues/1343

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/886

js/ui/extensionDownloader.js

@@ -198,9 +198,6 @@ class InstallExtensionDialog extends ModalDialog.ModalDialog {
 
         let content = new Dialog.MessageDialogContent({
             title: _("Download and install “%s” from extensions.gnome.org?").format(info.name),
-            icon: new Gio.FileIcon({
-                file: Gio.File.new_for_uri(`${REPOSITORY_URL_BASE}${info.icon}`),
-            }),
         });
 
         this.contentLayout.add(content);