benchmark: refactor deepequal-buffer

This is a minor refactor of benchmark/assert/deepequal-buffer.js to
reduce exceptions that need to be made for lint compliance.

PR-URL: https://github.com/nodejs/node/pull/21030


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>