test: remove 3rd argument from assert.strictEqual

If there is an AssertionError, the string literal is printed and not the
value of `r`. For debugging purposes, it is good to know if `r` is false
or null or something else.

PR-URL: https://github.com/nodejs/node/pull/19707


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>