Fixed license for all basic types

Just a simple fix and nobody will bother to do it next time.
We do not want to add `Microsoft Public License (Ms-PL)` to every file.  The normal MonoGame license header is only:

```
// MonoGame - Copyright (C) The MonoGame Team
// This file is subject to the terms and conditions defined in
// file 'LICENSE.txt', which is part of this source code package.
```

Nothing more is necessary.