## Description 

Due to a bug, that is now fixed in Runtime 1900, the AtStake storage items, which are used to compute the delegation payouts, were not properly removed after the end of the payouts.
This proposal is to remove those AtStake storage items.

## Technical details

In order to avoid generating big PoV, the cleanup is split into batches which are scheduled to execute 1 block after the other.  
To better understand the keys being used:

encoded key details
```
xxHash(ParachainStaking): a686a3043d0adcf2fa655e57bc595a78
xxHash(AtStake): f2ea452256cacfadf13b115a94c4029c
```

## Verification

Script used https://github.com/PureStake/moonbeam-tools/blob/0cd51e0950bc4553801b97c1917324aaeab5970e/src/hotfixes/runtime-1900-fix-at-stake-old-rounds.ts

Command to verify: `ts-node src/hotfixes/runtime-1900-fix-at-stake-old-rounds.ts --url wss://wss.moonriver.moonbeam.network --at-block 2918208`

```
[#2918208] Starting: {"current":6619,"first":2917800,"length":600}
Queried 1000...
Queried 2000...
Queried 3000...
Found 3143 keys through 1803 rounds (oldest: 1, most recent: 6606)
Applying batch limits: [storage: 500kB, extrinsic: 500kB, calls: 500]
propose batch 0 for block +1: [Rounds: 500 - Candidates: 1399 - Extrinsic: 26kB - Storage: 197kB]
propose batch 1 for block +2: [Rounds: 500 - Candidates: 708 - Extrinsic: 26kB - Storage: 309kB]
propose batch 2 for block +3: [Rounds: 133 - Candidates: 147 - Extrinsic: 7kB - Storage: 498kB]
propose batch 3 for block +4: [Rounds: 88 - Candidates: 134 - Extrinsic: 4kB - Storage: 496kB]
propose batch 4 for block +5: [Rounds: 119 - Candidates: 137 - Extrinsic: 6kB - Storage: 499kB]
propose batch 5 for block +6: [Rounds: 106 - Candidates: 144 - Extrinsic: 5kB - Storage: 497kB]
propose batch 6 for block +7: [Rounds: 167 - Candidates: 194 - Extrinsic: 8kB - Storage: 498kB]
propose batch 7 for block +8: [Rounds: 135 - Candidates: 153 - Extrinsic: 7kB - Storage: 499kB]
propose batch 8 for block +9: [Rounds: 55 - Candidates: 127 - Extrinsic: 2kB - Storage: 447kB]
propose all-in batch Extrinsic: 92kB - hash: 0xd3eca41010865bb65d6eaa057681a9ea9dcba8bb1ee7861a8c4e956beeb93263
```


Send a batch of dispatch calls and atomically execute them.
The whole transaction will rollback and fail if any of the calls failed.

May be called from any origin.

- `calls`: The calls to be dispatched from the same origin. The number of call must not
  exceed the constant: `batched_calls_limit` (available in constant metadata).

If origin is root then call are dispatch without checking origin filter. (This includes
bypassing `frame_system::Config::BaseCallFilter`).

# <weight>
- Complexity: O(C) where C is the number of calls to be batched.
# </weight>

- There was a bug in the computer program that caused some storage items to not be removed properly.
- The bug has been fixed in a new version of the program.
- To fix the problem, the program will remove the storage items in batches, one after the other.
- A script was used to verify that the fix worked correctly.
- The fix will be applied in the next block.

#117 Technical Cleanup: Remove old AtStake storage items

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