Log Message:
Revert "security/gnutls: Use system TLS trust anchors."

This requires review of how SmartOS and macOS, at least, are supposed
to handle TLS trust anchors for pkgsrc, which I didn't do -- it's
practically guaranteed that referring to
share/mozilla-rootcerts/cacert.pem is wrong on those platforms like
it is on NetBSD, but I don't know offhand what the right alternative
is and this can hold off until we determine that.