test: remove test messages for assert.strictEqual

Remove test messages for assert.strictEqual,
as the default messages are a better option.

PR-URL: https://github.com/nodejs/node/pull/15995


Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>