crossposter exposes its allow list on error

[us3r1d]

When you try to add a Mastodon account from an instance that's not in the ${ALLOWED_DOMAIN} list, the error message includes the list of allowed domains.

My install is at https://xpost.oksocial.net/; you can see the behavior there.

Can we get that removed, or at least an option to not include it?