Remove '_'+file.name

Why Form.prototype.toFormData appends '_'+file.name?

When upload request body looks like:

------WebKitFormBoundary13nJwlOAdYFVK3qi
Content-Disposition: form-data; name="file"; filename="949A0453.JPG"
Content-Type: image/jpeg


------WebKitFormBoundary13nJwlOAdYFVK3qi
Content-Disposition: form-data; name="_file"

949A0453.JPG
------WebKitFormBoundary13nJwlOAdYFVK3qi--