chore: Remove legacy key handling on ComboBoxItems

src/Uno.UI/UI/Xaml/Controls/ComboBox/ComboBoxItem.cs

@@ -14,31 +14,6 @@ public ComboBoxItem()
 			DefaultStyleKey = typeof(ComboBoxItem);
 		}
 
-		protected override void OnKeyDown(KeyRoutedEventArgs args)
-		{
-			if (ItemsControl.ItemsControlFromItemContainer(this) is ComboBox comboBox)
-			{
-				if ((args.Key is VirtualKey.Enter or VirtualKey.Space) && comboBox.IsDropDownOpen)
-				{
-					var item = comboBox.ItemFromContainer(this);
-					if (item != null)
-					{
-						comboBox.SelectedItem = item;
-						comboBox.IsDropDownOpen = false;
-						args.Handled = true;
-					}
-				}
-
-				if (!args.Handled)
-				{
-					// Fallback to combobox keydown handling
-					args.Handled = comboBox.TryHandleKeyDown(args, this);
-				}
-			}
-
-			base.OnKeyDown(args);
-		}
-
 		internal void ChangeVisualStateInternal(bool useTransitions) => ChangeVisualState(useTransitions);
 
 		private protected override void ChangeVisualState(bool useTransitions)