Sorry for my slow answer. I’m away from my computer (vacation) – which means I can’t verify what I’m telling you 😉 But look in the Edit menu. There’s something called “back-delete” or something like that – that should do the trick.
Only thing is that it will delete Originals too – so be aware of that. Of cause if that happens by accident, you can always just Undo.
I hope this helps!