doc: remove redundant table of contents for N-API

Since the table of contents is built dynamically when
building the documentation, the additional table of
contents is redundant and an extra overhead to maintain.

PR-URL: https://github.com/nodejs/node/pull/20395


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>