So, technically, yes... you /can/ delete.
However: Do the relays honor that? Does the delete request reach enough relays to propagate across the network? Chances are a blastr relay has sent it into one random af corner of the internet and at some point propagates the event right back into the network.
tl;dr: Don't rely on it. If you have only just posted it and immediately send the delete request you MIGHT be lucky. Might, perhaps, potentially. 

 The delete request stays on the server. Clients should re-broadcast that delete event. Still no guarantee, of course.