cleanup: Use some more array destructuring

Array destructuring has been supported by gjs/mozjs for quite some time,
so we are already using it heavily where it makes sense.

However one place still sneaked through where using destructuring makes
sense, as the element's position has semantic meaning (instead of just
making it the first, second, ... element).

https://gitlab.gnome.org/GNOME/gnome-shell-extensions/merge_requests/91

extensions/places-menu/placeDisplay.js

@@ -495,7 +495,7 @@ var PlacesManager = class {
         for (let i = 0; i < lines.length; i++) {
             let line = lines[i];
             let components = line.split(' ');
-            let bookmark = components[0];
+            let [bookmark] = components;
 
             if (!bookmark)
                 continue;