Noticed that I've been missing this since the beginning of time when
porting some ancient inline-C.

We already have obj.uncacheable und obj.hits in vcl_deliver, so not
having these seems arbitrary. Copying out the values in vcl_hit just
to have them available in vcl_deliver, as it was possible previously,
implies unnecessary overhead.

One use case is to extend object lifetime downstream when delivering a
stale object, e.g.

sub vcl_deliver {
    if (! obj.uncacheable && obj.ttl < 0s) {
	set resp.http.Expires = now + 1m;
	set resp.http.Cache-Control = "public, max-age=60";
	unset req.http.Age;
    }
}

merges #2057