Reap stash for an un-decodable staking ledger

[Ank4n]

Some configuration changes can lead to StakingLedger in an inconsistent state. For example, this PR paritytech/substrate#12343 introduced MaxUnlockingChunks that if reduced abruptly, can make the StakingLedger undecodable.

An action we could take here is allow reap_stash to kill this stash if the ledger is an inconsistent state.

Concerns:
The stash could be of high value and an inconsistent state could be due to an configuration change not intended to corrupt the ledger. If the ledger is recoverable in future, one might want to fix that or handle it in a proper migration. Once stash is reaped, it won't be recoverable.

cc: @kianenigma

[kianenigma]

As a starting point, I suggest we run the try_state of staking on Polkadot and Kusama, and make sure all the assertions there are correct. Then, we can incorporate un-decodable ledger into the try_state hook of staking as well.