[NUI] Fix to invoke SelectedChanged when IsSelected is changed by setter

[NUI] Fix to invoke SelectedChanged when IsSelected is changed by setter

Previously, SelectedChanged was not invoked when IsSelected is changed
by IsSelected's setter.
e.g. checkBox.IsSelected = true;

The issue occurred due to the logic that checked mouse up and key up.

Now, the incorrect logic has been removed and SelectedChanged is invoked
when IsSelected is changed by ISelected's setter.