I just asked a question that was closed as off-topic. I flagged it for migration, but then decided I didn't want to wait, so I just reposted the question on programmers.SE. Do I need to cancel the migration request? I read some other answers indicating that questions can't be "unflagged", but I just want to make sure there's nothing else I have to do to prevent migration on this one.
Since there are no answers in the SO version of your question, you can simply delete it. You should also post a comment there saying that you are deleting it because you cross posted on Programmers, so the moderator responding to your flag knows what happened.
If you couldn't delete the question yourself, you should have re-flagged it and ask for it to be deleted, again explaining why.
And... Don't do that again.