doc: fix unassigned deprecation code

Forgot to assign the deprecation code when landing
1f8d527e

PR-URL: https://github.com/nodejs/node/pull/15741


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>