I created an account at Stack Exchange and realized that I don't need it and can use Gmail to log in instead. I tried clicking the x under my logins but it says "you can't remove your only login"
This blog post doesn't apply to Stack Exchange OpenID.
You can let it sit if you like. It's not really hurting anything. If you do want to remove it, though, just let us know. Make it clear that you want to delete the Stack Exchange OpenID account (and give us the email address it's associated with) and not your site profile.