doc: 移除不使用的命名空间

Author: ArgoZhang

src/BootstrapBlazor/Components/Textarea/Textarea.razor.cs

@@ -3,8 +3,6 @@
 // See the LICENSE file in the project root for more information.
 // Maintainer: Argo Zhang([email protected]) Website: https://www.blazor.zone
 
-using Microsoft.AspNetCore.Components.Web;
-
 namespace BootstrapBlazor.Components;
 
 /// <summary>