[EOSIO/eos] Thrashed multi_index (added secondary after table content). How can I recover RAM? (#5307)

Sure.

Here is the old:
«`
/// @abi table score i64
struct score {
uint64_t transaction_id;
int64_t final_distance;
int64_t leo_displacement;
int64_t target_displacement;

uint64_t mission_id;

uint64_t primary_key() const { return transaction_id; }
uint64_t by_mission_id() const { return mission_id; }

EOSLIB_SERIALIZE(
score,
(transaction_id)(final_di