test: remove custom error message

Default error message contains the actual and expected values,
which is more informative than the custom error message to be deleted.

PR-URL: https://github.com/nodejs/node/pull/19526


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Shingo Inoue <leko.noor@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>