Some callers, like `construct_range_to_endpoint_map` for describe_ring,
or `get_secondary_ranges` for alternator ttl pass vnode tokens (the
vnodes' start token), and therefore can benefit from the fast lookup
path in `vnode_effective_replication_map::do_get_replicas`.
Otherwise the vnode token is binary-searched in sorted_tokens using
token_metadata::first_token().
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>