There is no way to delete a poll after having created one. This is problematic because it means there can be ZERO mistakes before hitting that final Enter key to submit the poll. I need to create a poll in a channel with around 100 users and it won't be acceptable to spam the channel with several poll attempts. I'm looking into other polls because of this and the fact that I can't edit after the fact.
I agree: editing polls in slack would be a nice feature. I will put it to our backlog.
You should be able to delete polls in slack like you can delete normal messages. This can be done in 'More actions' if you hover the poll in slack.
It is now possible to delete a poll in slack, after it is created as long as nobody has voted yet.