Enable ApprovalCheckingVotingRule on Polkadot

[ordian]

Before we deploy enable parachains runtime on Polkadot

polkadot/runtime/polkadot/src/lib.rs

Lines 1185 to 1242 in 59e9480

	impl primitives::v1::ParachainHost<Block, Hash, BlockNumber> for Runtime {
	fn validators() -> Vec<ValidatorId> {
	Vec::new()
	}
	fn validator_groups() -> (Vec<Vec<ValidatorIndex>>, GroupRotationInfo<BlockNumber>) {
	(Vec::new(), GroupRotationInfo { session_start_block: 0, group_rotation_frequency: 0, now: 0 })
	}
	fn availability_cores() -> Vec<CoreState<Hash, BlockNumber>> {
	Vec::new()
	}
	fn persisted_validation_data(_: Id, _: OccupiedCoreAssumption)
	-> Option<PersistedValidationData<Hash, BlockNumber>> {
	None
	}
	fn check_validation_outputs(_: Id, _: primitives::v1::CandidateCommitments) -> bool {
	false
	}
	fn session_index_for_child() -> SessionIndex {
	0
	}
	fn session_info(_: SessionIndex) -> Option<SessionInfo> {
	None
	}
	fn validation_code(_: Id, _: OccupiedCoreAssumption) -> Option<ValidationCode> {
	None
	}
	fn candidate_pending_availability(_: Id) -> Option<CommittedCandidateReceipt<Hash>> {
	None
	}
	fn candidate_events() -> Vec<CandidateEvent<Hash>> {
	Vec::new()
	}
	fn dmq_contents(
	_recipient: Id,
	) -> Vec<InboundDownwardMessage<BlockNumber>> {
	Vec::new()
	}
	fn inbound_hrmp_channels_contents(
	_recipient: Id
	) -> BTreeMap<Id, Vec<InboundHrmpMessage<BlockNumber>>> {
	BTreeMap::new()
	}
	fn validation_code_by_hash(_hash: ValidationCodeHash) -> Option<ValidationCode> {
	None
	}
	}

we need to revert #3321.

[ordian]

after #3815 is merged, but before it's enacted, we'd need a client release with this fix

[rphmeier]

I think even after it's enacted is OK. Because there won't be any parachains, the voting rule will still effectively be longest-chain until relay-chain governance actually adds a parachain.