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/runDialog.js

@@ -239,7 +239,7 @@ class RunDialog extends ModalDialog.ModalDialog {
         this._errorMessage.set_text(message);
 
         if (!this._errorBox.visible) {
-            let [errorBoxMinHeight, errorBoxNaturalHeight] = this._errorBox.get_preferred_height(-1);
+            let [, errorBoxNaturalHeight] = this._errorBox.get_preferred_height(-1);
 
             let parentActor = this._errorBox.get_parent();
             Tweener.addTween(parentActor,