Migrate pallet-preimage to benchmark v2

[AurevoirXavier]

Part of:

• Refactor pallets to V2 bench syntax #6202.

[ggwpez]

Why is this an expect now? The pallet is also usable without manager origin.
It returned BenchmarkError::Weightless before.

[AurevoirXavier]

I think that error is meaningless.

Same as:

polkadot-sdk/substrate/frame/treasury/src/benchmarking.rs

Lines 121 to 126 in 06debd0

	let origin =
	T::SpendOrigin::try_successful_origin().map_err(|_| BenchmarkError::Weightless)?;
	let beneficiary = T::Lookup::lookup(beneficiary_lookup.clone()).unwrap();
	#[extrinsic_call]
	_(origin as T::RuntimeOrigin, value, beneficiary_lookup);

It was not part of the benchmark(#[extrinsic_call]) code block. Additionally, I believe the original .expect message is more readable. So I reuse it.

What do you suggest?

[AurevoirXavier]

Also can be found here

polkadot-sdk/substrate/frame/lottery/src/benchmarking.rs

Line 50 in 06debd0

.expect("ManagerOrigin has no successful origin required for the benchmark");