title: simple form duplicate input
body: <p>I'm using ruby simple_form to generate a form with a checkbox in it. The form is rendered with:</p>
  
  <pre><code>&lt;%= simple_form_for(@user) do |f| %&gt;
    &lt;%= f.input :receive_notifications, as: :boolean, label: 'Receive Notifications' %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>This outputs the html:</p>
  
  <pre><code>&lt;form accept-charset="UTF-8" action="/admin/users/9" class="simple_form edit_user" id="edit_user_9" method="post" novalidate="novalidate"&gt;
    &lt;div style="display:none"&gt;
      &lt;input name="utf8" type="hidden" value="✓"&gt;
      &lt;input name="_method" type="hidden" value="patch"&gt;
      &lt;input name="authenticity_token" type="hidden" value="m2rM8t/lZ1g3UfYER4xFiNkHKpDX5GrpjdapQCLPKHQ="&gt;
    &lt;/div&gt;
    &lt;div class="form-group boolean optional user_receive_notifications"&gt;
      &lt;input name="user[receive_notifications]" type="hidden" value="0"&gt;
      &lt;label class="boolean optional control-label checkbox" for="receive_notifications"&gt;
        &lt;input checked="checked" class="boolean optional" id="user_receive_notifications" name="user[receive_notifications]" type="checkbox" value="1"&gt;Receive Notifications
      &lt;/label&gt;
    &lt;/div&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>The question is, how do I get rid of that duplicate input inside the form-group?</p>
  
  <p>Edit:
  Form Data from browser inspector:</p>
  
  <p>utf8:✓</p>
  
  <p>_method:patch</p>
  
  <p>authenticity_token:m2rM8t/lZ1g3UfYER4xFiNkHKpDX5GrpjdapQCLPKHQ=</p>
  
  <p>user[receive_notifications]:0</p>
  
  <p>user[receive_notifications]:1</p>