js: Remove unused catch bindings

Optional catch bindings have been supported for quite a while now,
so we can treat unused error bindings in catch statements like any
other unused variable.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3684>

js/ui/extensionDownloader.js

@@ -88,7 +88,7 @@ export function uninstallExtension(uuid) {
         const updatesDir = Gio.File.new_for_path(GLib.build_filenamev(
             [global.userdatadir, 'extension-updates', extension.uuid]));
         FileUtils.recursivelyDeleteDir(updatesDir, true);
-    } catch (e) {
+    } catch {
         // not an error
     }