Remove candidate selection (#3148)

* Create validator_side module

* Subsume Candidate Selection

* Add test to ensure candidate backing logic is correct

* Ensure secondings are adequately cleaned up and address test flakyness

* Address Feedback

polkadot/node/service/src/lib.rs

@@ -447,7 +447,6 @@ where
 	use polkadot_availability_bitfield_distribution::BitfieldDistribution as BitfieldDistributionSubsystem;
 	use polkadot_node_core_bitfield_signing::BitfieldSigningSubsystem;
 	use polkadot_node_core_backing::CandidateBackingSubsystem;
-	use polkadot_node_core_candidate_selection::CandidateSelectionSubsystem;
 	use polkadot_node_core_candidate_validation::CandidateValidationSubsystem;
 	use polkadot_node_core_chain_api::ChainApiSubsystem;
 	use polkadot_node_collation_generation::CollationGenerationSubsystem;
@@ -486,11 +485,6 @@ where
 			keystore.clone(),
 			Metrics::register(registry)?,
 		),
-		candidate_selection: CandidateSelectionSubsystem::new(
-			spawner.clone(),
-			keystore.clone(),
-			Metrics::register(registry)?,
-		),
 		candidate_validation: CandidateValidationSubsystem::with_config(
 			candidate_validation_config,
 			Metrics::register(registry)?,