DelegateCommand is not rely CommandManager.RequerySuggested anymore

[Ted-Zhang]

By reading the ReadMe file, I think there is not accurate anymore, the DeletegateComand is not rely on CommandManager.RequestSuggest anymore, it use RaiseCanExecuteChanged or ObservesProperty to raise the event.

https://github.com/PrismLibrary/Prism/blob/master/Source/Prism/Commands/DelegateCommandBase.cs