title: API call field delete with delete_values parameter not working
body: <p>When performing an API call to delete a field in an app, the field is deleted at the template level. However the <em>delete_values</em> parameters is not doing the job when setting it up to <em>true</em></p>
  
  <pre><code>## my python code using the requests library
  url = 'https://api.podio.com/app/16200981/field/125619360'
  data = {'delete_values': True}
  request = requests.delete(url, headers=self._get_headers(), data=data)
  </code></pre>
  
  <p>The call is a success with a response body</p>
  
  <pre><code>{"revision": 29}
  </code></pre>
  
  <p>However none of the item's values for this field are deleted.</p>