Boolean single on/off field - how to make it NOT render the off option?
You can hide them either through CSS or you can unset them using the form_alter if you are using forms. Look at the code below 
In this code, I am unsetting the author on the comment form.

function Mymodulename_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  switch($form_id) {
    if($form_id == 'comment_form) {
      unset($form['author']);
    }
  }
}


If you've added the field to some node then you can unset them using this code. 

unset($node-&gt;field);