feat: clean up warnings.

demo/Ursa.Demo/Views/MainView.axaml.cs

@@ -1,7 +1,4 @@
-using Avalonia;
 using Avalonia.Controls;
-using Avalonia.Interactivity;
-using Avalonia.Styling;
 
 namespace Ursa.Demo.Views;
 
@@ -11,14 +8,4 @@ public partial class MainView : UserControl
     {
         InitializeComponent();
     }
-
-    private void ToggleButton_OnIsCheckedChanged(object? sender, RoutedEventArgs e)
-    {
-        var app = Application.Current;
-        if (app is not null)
-        {
-            var theme = app.ActualThemeVariant;
-            app.RequestedThemeVariant = theme == ThemeVariant.Dark ? ThemeVariant.Light : ThemeVariant.Dark;
-        }
-    }
 }

demo/Ursa.Demo/Views/MainWindow.axaml.cs

@@ -1,6 +1,3 @@
-using System;
-using Avalonia.Controls;
-using Avalonia.Interactivity;
 using Ursa.Controls;
 
 namespace Ursa.Demo.Views;

demo/Ursa.Demo/Views/SingleView.axaml.cs

@@ -1,6 +1,4 @@
-using Avalonia;
 using Avalonia.Controls;
-using Avalonia.Markup.Xaml;
 
 namespace Ursa.Demo.Views;