Well, you could still add a delete button to make people feel better (I'm only half joking)
And as a potential user I'm only half-insulted.
But seriously, what purpose would it serve over a promise in TOS? A normal user will trust both (except the button would be bullshitting them). A privacy-obsessed one will trust neither.
You could make a delete button which merely opens a popup to explain that they do not save it in the first place. That way if they're looking for a delete button, they'll find it, but it will give them the right information.