Preimage requested twice for Referenda approved via Democracy

[bernardo-xxnet]

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Description of bug

When a Referendum is approved in the Democracy pallet, the preimage is held (requested) before the Scheduler is called.

substrate/frame/democracy/src/lib.rs

Line 1599 in 2520ded

T::Preimages::hold(&status.proposal);

The changes in #13340 make the Scheduler request a preimage for the call being scheduled.
This results in the preimage for any referendum passing via Democracy being requested twice.

When the Scheduled call runs, the preimage is unrequested only once, leaving a pending request for that preimage forever onchain.

This change is included in the latest release polkadot-v0.9.39.

I believe that the solution to this issue could be to not request the preimage in the Democracy pallet anymore, since the call to Scheduler will request it anyways.

Steps to reproduce

Run the dev network on Substrate branch polkadot-v0.9.3 and pass a proposal via Democracy.
After the proposal passes and is executed by the Scheduler, the preimage remains requested.

[bkchr]

Ty for the report! Good find!