Click on the controller that has the top bar navigate to the properties bar on the right hand side of Xcode. There is a drop down labeled Top Bar (as shown above) change this drop down to none.
You have to click the actual navigation controller, not the view controller. On the view controller the navigation drop down doesn't show up, but you can still achieve this by selecting Top Bar: none in Simulated Metrics.
In the Storyboard view, just select the NavigationController scene and UNCHECK Shows Navigation Bar (Attributes Inspector)