添加以下代码即可

<WindowChrome.WindowChrome>
    <WindowChrome GlassFrameThickness="0" ResizeBorderThickness="4" CaptionHeight="0" CornerRadius="0" />
</WindowChrome.WindowChrome>

具体的看下文档吧

https://docs.microsoft.com/zh-cn/dotnet/api/system.windows.shell.windowchrome?redirectedfrom=MSDN&view=netframework-4.5#%E5%AE%9A%E4%B9%89