Remove Microsoft.Xna.Framework.Graphics.DeviceType.

The Microsoft.Xna.Framework.Graphics.DeviceType enum was removed after XNA 3.1. I couldn't find anything in MonoGame that was using it. If anything outside of MonoGame were, it'd be using an overload of GraphicsDevice that accepted a DeviceType parameter, which doesn't exist.

In my project, the name DeviceType is ambigious with Microsoft.DirectX.DirectInput.DeviceType. I'm attempting to achieve compile-time parity porting from XNA to MonoGame, which is why I'm relying on the DirectX assemblies.