Have you considered approaching this problem from a different angle?
Rather than trying to avoid loading the Javascript file, which could cause issues with caching, there is another solution. You can prevent the script from affecting your form by excluding it.
The *form_tabbing.js* script specifically targets form elements with the enableFormTabbing class:
<form class="enableFormTabbing">
<fieldset id="fieldset-[unique-id]">
<legend id="fieldsetlegend-[same-id-as-above]">Title</legend>
</fieldset>
</form>
All you have to do is ensure that your form does not have the enableFormTabbing class.
Since you are working with a Dexterity content type, my recommendation is to override the AddForm like this:
class AddForm(dexterity.AddForm):
"""Default view resembles a News Item.
"""
grok.name('collective.nitf.content')
grok.layer(INITFBrowserLayer)
enable_form_tabbing = False
By setting the enable_form_tabbing attribute in plone.app.z3cform, you gain control over tab functionality in your form.
This same approach can be applied to the EditForm as well.
I hope this information proves helpful!