One of my pet annoyances with CRM form editor in 2011 and 2013 has always been inconsistency in field handling. It is so easy to create a new field but impossible to delete one. Or so I thought, until MVP comrade Gonzalez showed me a very clever way to nuke a field. Instructions in a nutshell: remove field from the form, Save, Publish, add field back to the form, click Change Properties, Details tab, Edit button, then Action -> Delete command, Cancel, Cancel, get an error message, dismiss the error message. Voilà.