parachain-template: Simplify it (#3801)

Also while doing this, move slot duration fetching into the AURA code.

cumulus/client/consensus/aura/src/collators/basic.rs

@@ -42,7 +42,7 @@ use sp_api::{CallApiAt, ProvideRuntimeApi};
 use sp_application_crypto::AppPublic;
 use sp_blockchain::HeaderBackend;
 use sp_consensus::SyncOracle;
-use sp_consensus_aura::{AuraApi, SlotDuration};
+use sp_consensus_aura::AuraApi;
 use sp_core::crypto::Pair;
 use sp_inherents::CreateInherentDataProviders;
 use sp_keystore::KeystorePtr;
@@ -74,8 +74,6 @@ pub struct Params<BI, CIDP, Client, RClient, SO, Proposer, CS> {
 	pub para_id: ParaId,
 	/// A handle to the relay-chain client's "Overseer" or task orchestrator.
 	pub overseer_handle: OverseerHandle,
-	/// The length of slots in this chain.
-	pub slot_duration: SlotDuration,
 	/// The length of slots in the relay chain.
 	pub relay_chain_slot_duration: Duration,
 	/// The underlying block proposer this should call into.
@@ -197,11 +195,16 @@ where
 					Ok(Some(h)) => h,
 				};
 
+			let slot_duration = match params.para_client.runtime_api().slot_duration(parent_hash) {
+				Ok(d) => d,
+				Err(e) => reject_with_error!(e),
+			};
+
 			let claim = match collator_util::claim_slot::<_, _, P>(
 				&*params.para_client,
 				parent_hash,
 				&relay_parent_header,
-				params.slot_duration,
+				slot_duration,
 				params.relay_chain_slot_duration,
 				&params.keystore,
 			)