style: Avoid trailing commas in array destructuring

When destructuring multiple return values, we often use trailing commas
to indicate that there are additional elements that we are ignoring.

There isn't anything inherently wrong with that, but it's a style that's
too confusing for eslint - on the one hand we require a space after a
comma, on the other hand we require no space before closing brackets.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/607

js/ui/overviewControls.js

@@ -133,7 +133,7 @@ var SlidingControl = class {
 
     getVisibleWidth() {
         let child = this.actor.get_first_child();
-        let [, , natWidth, ] = child.get_preferred_size();
+        let [, , natWidth] = child.get_preferred_size();
         return natWidth;
     }