src: remove empty comment in node_http2.h

This commit removes an "empty" comment in node_http2.h that I don't
think was intentional and as far as I can tell not a doxygen comment or
anything like that.

This was not picked up by the cpp linter so a suggestion has also been
added to the CheckComment function to detect these in the future.

PR-URL: https://github.com/nodejs/node/pull/16400


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>