tools: use no-useless-concat ESLint rule

* Add `no-useless-concat: error` to .eslintrc.yaml.
* Apply no-useless-concat rule to tests.

PR-URL: https://github.com/nodejs/node/pull/12613


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>