Hide "Always display title" option on Submenu widget

After #3021497: Update Menu Block to menu_block-7.x-2.8, a new option has appeared on the settings for the Submenu widget: "Always display title." It's the second option shown (so, really pretty prominent) but it's really kind of an edge case. What it does, is it'll cause the widget to display it's title when it's empty. So, rather than just hiding the widget if it has no items to show, it show the widget title.

There's really no reason for such an edge case (which isn't useful in the 99% case) to be shown so prominently. We hide options on this and other widgets when we think they aren't useful enough - I think this one qualifies for that as well.

Let's hide that option! If a site really needs it, it can use a form alter to add it back. If we get this out quickly, this isn't really a regression since the release that first included it was released yesterday. :-)