I cannot for the life of me find the UI to delete an existing field definition. I must be blind or stupid, because I don't believe field definitions are forever, so there must be a way to delete them, if only to undo a newbie mistake. All I have achieved in 2 hours of squinting at the Form & Content Type page is how to move a field to the "unused" area on the right, but I can't delete it from there.
Halp?