Realistically, isn't it unlikely to be able to delete them from all the relays?
Discussion
Not really. I delete things all the time in my main account. Most relays support it. Some times there is a delay or it needs to be sent twice, but other than that deleting works quite well.
Finding all the relays that an event propagated to could be a problem. The event may appear to be deleted from your perspective, but not from others