title: UISearchController searchBar showsCancelButton not being respected
body: <p>I've added a UISearchController to my application and set it's searchBar to the <code>titleView</code> of my <code>navigationItem</code>. </p>
  
  <p>This works but I am seeing the cancel button despite having set <code>showsCancelButton</code> to <code>false</code>.</p>
  
  <pre><code>    searchController = UISearchController(searchResultsController: searchResultsController)
      searchController.searchResultsUpdater = searchResultsUpdater
  
  
      // Configure the searchBar
      searchController.searchBar.placeholder = "Find Friends..."
      searchController.searchBar.sizeToFit()
      searchController.searchBar.showsCancelButton = false
  
      self.definesPresentationContext = true
  
      navigationItem.titleView = searchController.searchBar
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/Uxu2t.png" alt="enter image description here"></p>