fix(dock): remove unused using and add event cleanup symmetry

src/Editor/Ghost.Editor/View/Controls/DockLayout.DragDrop.cs

@@ -1,6 +1,5 @@
 using Ghost.Core;
 using Ghost.Editor.Core.Controls.Internal.Docking;
-using Ghost.Editor.View.Windows;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 

src/Editor/Ghost.Editor/View/Windows/DockWindow.xaml.cs

@@ -27,6 +27,7 @@ internal sealed partial class DockWindow : WindowEx
         
         this.Closed += (s, e) => 
         {
+            PART_DockLayout.TabTornOff -= OnTabTornOff;
             if (_rootPropertyToken != 0)
             {
                 PART_DockLayout.UnregisterPropertyChangedCallback(DockLayout.RootProperty, _rootPropertyToken);