test: remove ambiguous error messages from test_error

assert.strictEqual accepts 3 arguments, the last of which allows for
user-specified error message to be thrown when the assertion fails.
Unfortunately, this error message is less helpful than the default when
it is vague. This commit removes vague, user-specified error messages,
instead relying on clearer, default error messages.

PR-URL: https://github.com/nodejs/node/pull/17812


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>