overview: Replace InfoBar with message tray notifications

The layout of recent mockups occupies the space previously reserved
for the info bar with the view selector. As the bar's purpose is
mainly to provide the user with feedback, it makes sense to use the
existing message tray facility instead of moving the bar elsewhere.

https://bugzilla.gnome.org/show_bug.cgi?id=634948

js/ui/placeDisplay.js

@@ -109,7 +109,7 @@ PlaceDeviceInfo.prototype = {
                 this._mount.unmount_finish(res);
         } catch (e) {
             let message = _("Failed to unmount '%s'").format(o.get_name());
-            Main.overview.infoBar.setMessage(message,
+            Main.overview.shellInfo.setMessage(message,
                                              Lang.bind(this, this.remove),
                                              _("Retry"));
         }