Removed PreferredInterfaceOrientationForPresentation() for iOS

Overriding this method is not something that is commonly required on iOS.

It also causes the following bug:

- Create a MonoGame game that runs in `LandscapeLeft` or `LandscapeRight`
- Play the game in `LandscapeLeft`
- Pull out the underlying `UIViewController` and present a native iOS controller via `PresentViewController`
- Dimiss the modal controller
- The MonoGame controller will return `LandscapeRight` for `PreferredInterfaceOrientationForPresentation()`
- Your game will be upside down.

Removing the method completely fixes the issue in our game.

I have not tested it, but I presume the same would happen with a portrait game when it is oriented `PortraitUpsideDown`.

Does anyone know if this method was overridden for a specific purpose? It is not commonly used in standard iOS apps. Apple doc here (might need to scroll down): http://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/Reference/Reference.html#//apple_ref/occ/instm/UIViewController/preferredInterfaceOrientationForPresentation