header.go
func (h *ResponseHeader) DelCookie(key string) {
	h.cookies = delAllArgs(h.cookies, key)
}
func (h *ResponseHeader) DelCookie(key string) {
	h.cookies = delAllArgs(h.cookies, key)
}
// DelCookie removes cookie under the given key from response header.
//
// Note that DelCookie doesn't remove the cookie from the client.
// Use DelClientCookie instead.