errors: replace `.split()` with `.replace()`

Replace a somewhat idiosyncratic use of `split()` to remove a prefix
with `replace()`. (A case could be made for `slice()` as well but I
think this is more readable.)

PR-URL: https://github.com/nodejs/node/pull/15545


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>