cleanup: Remove some unhelpful unused variables in destructuring

We aren't using them, and they don't add much in terms of clarity,
so drop them to fix a couple of eslint errors.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/627

js/ui/userWidget.js

@@ -103,8 +103,7 @@ class UserWidgetLabel extends St.Widget {
         let availWidth = box.x2 - box.x1;
         let availHeight = box.y2 - box.y1;
 
-        let [minRealNameWidth, minRealNameHeight,
-             natRealNameWidth, natRealNameHeight] = this._realNameLabel.get_preferred_size();
+        let [, , natRealNameWidth] = this._realNameLabel.get_preferred_size();
 
         if (natRealNameWidth <= availWidth)
             this._currentLabel = this._realNameLabel;