http.go
func (req *Request) RemoveMultipartFormFiles() {
	if req.multipartForm != nil {
		// Do not check for error, since these files may be deleted or moved
		// to new places by user code.
		req.multipartForm.RemoveAll()
		req.multipartForm = nil
	}
	req.multipartFormBoundary = ""
}
func (req *Request) RemoveMultipartFormFiles() {
	if req.multipartForm != nil {
		// Do not check for error, since these files may be deleted or moved
		// to new places by user code.
		req.multipartForm.RemoveAll()
		req.multipartForm = nil
	}
	req.multipartFormBoundary = ""
}
// RemoveMultipartFormFiles removes multipart/form-data temporary files
// associated with the request.