assert: use less read operations

This reduces the total amount of reads when using `assert.ok()` with
a falsy value. That increases the read performance significantly.

Also remove a comment that can not be addressed.

PR-URL: https://github.com/nodejs/node/pull/27525


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>