This is a method or sub-command of the Background command. It is not its own command.
This method of the background command can be used to delete a set leveling background. You cannot delete a custom leveling background if one has not been set yet. Deleting your custom leveling background will revert your leveling card back to the default 'Wavy Grey' background.
Deleting your custom background will delete it forever instantly. There is no way to recover the image. If you intend to keep your background for a later date, consider using the view method to save it.