bsdinstall: Drop Error from title in netconfig no interfaces dialog

This isn't inherently an error. It is if you're attempting to download
dist tarballs or later install packages, but a FreeBSD system with no
NIC is a reasonable setup to have, especially in a throwaway VM setting,
so we shouldn't say it is one.

Leaving the exit code as 1 is still fine, since auto will ignore it, and
avoids breaking other uses.

MFC after: 1 week

(cherry picked from commit 7414d14bd51d8378057bbe952c2715b9f32d1d3e)