Deprecate RewardDestination::Controller from staking

[rossbulat]

Deprecating this PR In favour of a lazy migration

• [x] Use this code when RewardDestination variant is removed.

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This PR removes the RewardDestination::Controller variant as a continuation of the controller account deprecation effort for staking.

Included is a migration that updates existing Controller payees to Account(controller).

• [x] Remove RewardDestination::Controller.
• [x] Migration to move RewardDestination::Controller to RewardDestination::Account(existing_controller).

Controller Payees to Migrate

The migration in this PR migrates every payee record, as Controller was index 3 and removing it therefore changes the encoding of the subsequent variants. Nevertheless, the actual Controller reward destinations that exist on the networks are as follows:

Polkadot: 706 Kusama: 571 Last updated: 07/07/2023 21:35 GMT+1

[stale[bot]]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[rossbulat]

bot rebase

[paritytech-processbot[bot]]

Error: Command 'Command { std: cd "/storage/repositories/substrate" && "git" "merge" "origin/master" "--no-ff" "--no-edit", kill_on_drop: false }' failed with status Some(1); output: no output

[rossbulat]

Closing in favour of https://github.com/paritytech/substrate/pull/14451/.