assert: improve AssertionError in case of "Errors"

Showing the stack trace in a error message obfuscates the actual
message and should not be visible therefore.

PR-URL: https://github.com/nodejs/node/pull/15025


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>