header.go
func (h *RequestHeader) DelCookie(key string) {
	h.parseRawHeaders()
	h.collectCookies()
	h.cookies = delAllArgs(h.cookies, key)
}
func (h *RequestHeader) DelCookie(key string) {
	h.parseRawHeaders()
	h.collectCookies()
	h.cookies = delAllArgs(h.cookies, key)
}
// DelCookie removes cookie under the given key.