Clear peers and online weight after 1 week of inactivity

[guilhermelawless]

To test, add this after L775 in node.cpp

store.online_weight_put (transaction, (std::chrono::system_clock::now () - std::chrono::hours (8 * 24)).time_since_epoch ().count (), nano::amount (1000));

Do we have any other way of reaching the last entry without using two iterators as I did?

[wezrule]

Do we have any other way of reaching the last entry without using two iterators as I did?

There is a way to use a reverse iterator in LMDB (maybe rocksdb as well I haven't checked), but we don't have any infrastructure wrapping it currently. I think this way is fine because online_weight only has 4032 keys and this is only called once on start-up.