Fix: removed useless key from relay_index

This field was never used except in debug messages (instead of using the
good value that is part of index_n).

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Fix: empty indexes_ht before destroying it.

Fixes: #722

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>