Remove deprecated collator-related code in cumulus

[RomarQ]

Removes collator-related code in cumulus, which has been deprecated for a long time.

Removes an old test, which was adapted in paritytech/cumulus#480 and duplicated by

polkadot-sdk/substrate/client/block-builder/src/lib.rs

Lines 389 to 415 in acac012

	fn block_building_storage_proof_does_not_include_runtime_by_default() {
	let builder = substrate_test_runtime_client::TestClientBuilder::new();
	let client = builder.build();
	let genesis_hash = client.info().best_hash;
	let block = BlockBuilderBuilder::new(&client)
	.on_parent_block(genesis_hash)
	.with_parent_block_number(0)
	.enable_proof_recording()
	.build()
	.unwrap()
	.build()
	.unwrap();
	let proof = block.proof.expect("Proof is build on request");
	let genesis_state_root = client.header(genesis_hash).unwrap().unwrap().state_root;
	let backend =
	sp_state_machine::create_proof_check_backend::<Blake2Hasher>(genesis_state_root, proof)
	.unwrap();
	assert!(backend
	.storage(&sp_core::storage::well_known_keys::CODE)
	.unwrap_err()
	.contains("Database missing expected key"),);
	}

PoV Recovery Test Updates

Updates the PoV recovery test (cumulus/zombienet/zombienet-sdk/tests/zombie_ci/pov_recovery.rs) to use a more realistic consensus mechanism:

Changes Made

• Removed: --use-null-consensus flag from test configuration

Rationale

Previous behavior (with null consensus):

• Nodes operated without real block production
• PoV recovery mechanisms triggered more frequently
• Created artificial test conditions that don't reflect production scenarios

New behavior (with actual consensus):

• Nodes produce blocks normally but don't announce them to peers
• PoV recovery occurs at a more realistic frequency
• Better simulates real-world network conditions where blocks may be missed

Impact

This change makes the test more representative of actual network conditions while maintaining the core functionality being tested.

Follow-up

Remove the following lines:

polkadot-sdk/cumulus/pallets/parachain-system/src/lib.rs

Lines 993 to 994 in 4acb964

	// TODO: Remove after https://github.com/paritytech/cumulus/issues/479
	sp_io::storage::set(b":c", &[]);

Review notes

I recommend enabling Hide whitespace option when reviewing the changes:

[RomarQ]

Once #9695 gets merged, will merge the changes here.

[RomarQ]

@lrubasze since you fixed the flakiness and enabled the pov_recovery zombienet tests recently, could you also have a look at the changes in this PR?