stop reporting "internal paths" during bootstrap

bootstrap_status_to_string() can report "internal paths" when the consensus actually contains exits, because it's conditional on router_have_consensus_path() which checks descriptors. In the cold cache case, there are likely no existing descriptors, so tor will give the misleading impression that the consensus lacks exits (when it's actually more likely that it simply hasn't gotten around to downloading enough descriptors yet).

Removing the code that handles these conditions also simplifies bootstrap_status_to_string().

This probably needs a tor-spec update.