refactor: remove useless reference

A reference to the initial IncomingMessage object (the first HTTP
request of the session) is kept in memory by default (`socket.request`),
so its attached ServerResponse object (`req.res`) would not be
garbage-collected. This will now be the case.

Note: the IncomingMessage object is needed in two cases:

- when working with the `express-session` middleware (`request.session`)
- when fetching the certificate of the client with `request.socket.getPeerCertificate()`

That's why removing it would be a breaking change.

lib/transports-uws/polling.ts

@@ -55,6 +55,8 @@ export class Polling extends Transport {
    */
   onRequest(req) {
     const res = req.res;
+    // remove the reference to the ServerResponse object (as the first request of the session is kept in memory by default)
+    req.res = null;
 
     if (req.getMethod() === "get") {
       this.onPollRequest(req, res);

lib/transports/polling.ts

@@ -54,6 +54,8 @@ export class Polling extends Transport {
    */
   onRequest(req: IncomingMessage & { res: ServerResponse }) {
     const res = req.res;
+    // remove the reference to the ServerResponse object (as the first request of the session is kept in memory by default)
+    req.res = null;
 
     if ("GET" === req.method) {
       this.onPollRequest(req, res);