docs: update 8.5.0 changelog

The original changelog included incorrect information regarding
the new perf_hooks api.

refs: nodejs/node#15308 (comment)

PR-URL: nodejs/node#15384
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: MylesBorins