doc: deprecation clarifications

PR-URL: https://github.com/nodejs/node/pull/19522


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>