doc: simplify deprecation language

Change instances of `foo has been deprecated` to `foo is deprecated` and
similar.

PR-URL: https://github.com/nodejs/node/pull/21136


Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>