cleanup: Don't shadow variables

Having variables that share the same name in overlapping scopes is
confusing and error-prone, and is best avoided.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/805

js/ui/dash.js

@@ -481,7 +481,7 @@ var Dash = GObject.registerClass({
         let appIcon = new DashIcon(app);
 
         appIcon.connect('menu-state-changed',
-                        (appIcon, opened) => {
+                        (o, opened) => {
                             this._itemMenuStateChanged(item, opened);
                         });