misc: remove unused ViewModel references from demo pages.

demo/Ursa.Demo/Pages/ElasticWrapPanelDemo.axaml.cs

@@ -1,5 +1,4 @@
 using Avalonia.Controls;
-using Ursa.Demo.ViewModels;
 
 namespace Ursa.Demo.Pages;
 
@@ -8,6 +7,5 @@ public partial class ElasticWrapPanelDemo : UserControl
     public ElasticWrapPanelDemo()
     {
         InitializeComponent();
-        DataContext = new ElasticWrapPanelDemoViewModel();
     }
 }