refactor: 移除变量

Author: ArgoZhang

src/BootstrapBlazor/Components/Dropdown/Dropdown.razor.cs

@@ -205,8 +205,6 @@ public partial class Dropdown<TValue>
     /// </summary>
     private bool _isAsyncLoading;
 
-    private readonly List<ComponentBase> _items = [];
-
     /// <summary>
     /// OnParametersSet 方法
     /// </summary>