test: remove duplicate test-child-process-execfilesync-maxBuffer.js

In addition correct the comment about what it does.

PR-URL: https://github.com/nodejs/node/pull/28139


Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>