Partial revert "tls: keep track of stream that is closed"

This partually reverts commit 4cdb0e89.

A nullptr check in TSLWrap::IsAlive() and the added test were left.

PR-URL: https://github.com/nodejs/node/pull/11947


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>