rewrite vote credits redemption to eat from rewards_pools on an epoch-sensitive basis (#4775)

* move redemption to rewards pools

* rewrite redemption, touch a few other things

* re-establish test coverage

core/src/staking_utils.rs

@@ -145,7 +145,6 @@ pub(crate) mod tests {
 
         let leader_stake = Stake {
             stake: BOOTSTRAP_LEADER_LAMPORTS,
-            epoch: 0,
             ..Stake::default()
         };