doc: do not identify string as "JavaScript string"

A parameter that is explicitly identified as a string does not need to
be further specified in the text as a "JavaScript string". Remove the
type altogether as it is indicated in the argument description.

PR-URL: https://github.com/nodejs/node/pull/19689


Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>