js: Drop tweener.js

We're using clutter's animation framework now, so lets drop the old
tweener support layer.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1200

js/ui/screenShield.js

@@ -345,7 +345,7 @@ var ScreenShield = class {
         this._lockDialogGroup.remove_all_transitions();
 
         if (animate) {
-            // Tween the lock screen out of screen
+            // Animate the lock screen out of screen
             // if velocity is not specified (i.e. we come here from pressing ESC),
             // use the same speed regardless of original position
             // if velocity is specified, it's in pixels per milliseconds