src: fix compile warnings introduced in 73ad3f9b

Fix warnings introduced in commit 73ad3f9b ("inspector: Fix crash for
WS connection"):

* add missing `override` keywords
* remove unused fields and functions

PR-URL: https://github.com/nodejs/node/pull/17649


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>