test: remove common.fileExists()

test-trace-event-promises.js was added to the codebase between the last
CI for https://github.com/nodejs/node/pull/22151 and it landing.

PR-URL: https://github.com/nodejs/node/pull/22200
Refs: https://github.com/nodejs/node/pull/22151


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>