保留antd的upload的功能：当上传照片数到达限制后，上传按钮消失。

[dayuy]

https://github.com/formilyjs/antd/blob/90556abf2680973881e2b43b6943ea08d2f920e6/packages/components/src/upload/index.tsx#L182 这里的 getPlaceholder(props) 默认children能否去掉，来保留原antd功能：upload在上传照片数量达到上限后，上传按钮自动消失（https://ant.design/components/upload-cn ）

<AntdUpload {...useUploadProps(props)}>
    {props.children || getPlaceholder(props)}
</AntdUpload>

原antd此功能：

<Upload
    action="https://www.mocky.io/v2/5cc8019d300000980a055e76"
    listType="picture-card"
    fileList={fileList}
    onPreview={handlePreview}
    onChange={handleChange}
>
        {fileList.length >= 8 ? null : uploadButton}
</Upload>

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