This function had a bug in stable (fixed in dev) when `last` returns
npos, but the function also appears to basically be duplicating what the
next split version can do, so this just removes it and uses the single
more generic split(strview, strview) method.
* make it so that we don't set up unbound resolver when we have no resolvers provided by config
* clean up dns codepath and make it use llarp::SockAddr instead of llarp::IpAddress
