removeCookie method
Removes a cookie by setting its value to an empty string and expiration to a past date.
key - The name of the cookie to be removed.
Implementation
void removeCookie(String key) {
key = fixCookieName(key);
_rq.cookies.removeWhere((element) => element.name == key);
_rq.response.cookies.removeWhere((element) => element.name == key);
}