Remove legacy network code (#860)

* expunge legacy code from polkadot-network

* mostly rip out old legacy protocol from service

* ensure validation work is spawned by incoming messages

* decouple availabliity store from network logic; clean up data flow

* av_store: test helpers and use futures-abort

* update polkadot-validation to pass n_validators when submitting chunks

* fallible erasure-chunk fetching

* implement `ErasureNetworking` for new network prot

* API for registering availability store in network

* fully integrate new network service into service

* fix validation tests

* scaffolding for porting collator over to new network

* track connected validators' peer IDs and distribute collators' collations

* helper in network for fetching all checked statements

* fix adder-collator

* actually register notifications protocol

* Update service/src/lib.rs

* merge with master

polkadot/test-parachains/adder/collator/src/main.rs

@@ -104,9 +104,9 @@ impl BuildParachainContext for AdderContext {
 		self,
 		_: Arc<collator::PolkadotClient<B, E, R>>,
 		_: SP,
-		network: Arc<dyn Network>,
+		network: impl Network + Clone + 'static,
 	) -> Result<Self::ParachainContext, ()> {
-		Ok(Self { _network: Some(network), ..self })
+		Ok(Self { _network: Some(Arc::new(network)), ..self })
 	}
 }