Tracker issue for cleaning up non-paged claimed rewards

[Ank4n]

When changes in https://github.com/paritytech/substrate/pull/13023 gets released, we will be relying on StakingLedger.claimed_rewards for preventing double claims for older eras (before the release). This code can be cleaned up after 84 eras (~84 days in Polkadot and ~21 days in Kusama).

This issue will be used to track the progress of the PR, release and cleanup.