What a useful tip from Geoff Varosky. – Thanks Geoff!
First, you will want to select the first one you see in the window by clicking on it, both the checkbox, and the item itself so it is highlighted as shown… going to show you a neat little trick!
Now, scroll ALL the way to the bottom of the list, and select that, using your shift + click combination, and PRESTO! Everything has been unselected, except for the last item, which is just a simple click.