tls: do not confuse TLSSocket and Socket

Don't use "socket" to describe two different objects in the same
function.

PR-URL: https://github.com/nodejs/node/pull/25153


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>