Hi,

unfortunately I don't think that there is a command/option in order to disable or remove a similar imported control..I've found a post on UserVoice Ability to disable controls in nintex forms 2010 from CA – Customer Feedback for Nintex that asks for the same feature.

For SharePoint 2013 I've found the help page that explain how to remove a custom control, Removing a custom control, but that's not your situation because you haven't deployed any custom solution..