title: Emacs helm completion: how to turn off persistent-help_line?
body: <p>I'd like to use <code>helm</code> as a drop-in replacement for <code>display-completion-list</code>.
  The only issue is that it displays this line on top, which I don't want:</p>
  
  <p><code>C-z: I don't want this line here (keeping session)</code>. </p>
  
  <p>Here's the code to illustrate: </p>
  
  <pre><code>(helm :sources `((name . "Do you have?")
                   (candidates . ("Red Leicester"
                                  "Tilsit"
                                  "Caerphilly"
                                  "Bel Paese"
                                  "Red Windsor"
                                  "Stilton"))
                   (action . identity)
                   (persistent-help . "I don't want this line here"))
        :buffer "*cheese shop*")
  </code></pre>
  
  <p>I've tried setting <code>persistent-help</code> to nil, or not setting it at all, but it
  still appears. How can I turn it off?</p>