How to unlicense an image

You can't unlicence. But it's a free asset, so there is no harm done. 

And btw: the single click licence is probably a good thing, as very few people are complaining. I hate getting asked 25 times to accept this and that before doing basic operations. And I have to say, that I only once licenced an asset by error (I have several 100 in my licencing history). Even when being asked to confirm (anything that costs more than one credit!), many people simply confirm. That is because we are used to confirm simply many nonsense actions automatically. And then there are those who licence 10 assets in a row, before they see, that they licenced the assets. You should be aware, that the licence button does, what it says: Licencing!