Without having the source code version of Kentico CMS
, I do not believe you can remove the div from around the form control. By default, each form control is nested into DIV tag with EditingFormControlNestedControl css class.
This behavior is ensured in ~\CMSFormControls\EditingFormControl.cs file. The Div tag is not part of the form control itself but part of the class which is responsible for adding controls to page in mentioned class. I think that ASP.NET panel is represented as DIV tag in .NET and we are adding the control to this panel.