http2: remove unused using declarations node_http2

PR-URL: https://github.com/nodejs/node/pull/20420


Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>