doc: update benchmark doc

Benchmark for arrays no longer exists, but it was still referenced in
documentation.

Refs: https://github.com/nodejs/node/pull/21831

PR-URL: https://github.com/nodejs/node/pull/25367


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>