[stable2412] Fix feature bandersnatch-experimental (#7187)

Fix the CI issue on the stable2412 branch by deleting the
`bandersnatch-experimental` dependant code. Also fix some other CI
checks.

The Bandersnatch VRFs crate is not on crates-io, hence why it is not
included in the release
https://github.com/paritytech/polkadot-sdk/blob/a843d15e

/substrate/primitives/core/Cargo.toml#L73

The only upstream crate that depends on this is
`sp-consensus-sassafras`, but we dont release that. So hopefully CI goes
green.

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Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>