http2: use session kUpdateTimer from kUpdateTimer

Reduces duplicated logic.

PR-URL: https://github.com/nodejs/node/pull/17704
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

lib/internal/http2/core.js

@@ -1343,8 +1343,8 @@ class Http2Stream extends Duplex {
       return;
     if (this[kTimeout])
       _unrefActive([kTimeout]);
-    if (this[kSession] && this[kSession][kTimeout])
-      _unrefActive(this[kSession][kTimeout]);
+    if (this[kSession])
+      this[kSession][kUpdateTimer]();
   }
 
   [kInit](id, handle) {