Remove real-overseer 🎉 (#2834)

* remove real-overseer

* overseer: only activate leaves which support parachains

* integrate HeadSupportsParachains into service

* remove unneeded line

polkadot/node/overseer/examples/minimal-example.rs

@@ -27,13 +27,19 @@ use futures::{
 use futures_timer::Delay;
 
 use polkadot_node_primitives::{PoV, BlockData};
-use polkadot_overseer::{Overseer, AllSubsystems};
+use polkadot_primitives::v1::Hash;
+use polkadot_overseer::{Overseer, HeadSupportsParachains, AllSubsystems};
 
 use polkadot_subsystem::{Subsystem, SubsystemContext, SpawnedSubsystem, FromOverseer};
 use polkadot_subsystem::messages::{
 	CandidateValidationMessage, CandidateBackingMessage, AllMessages,
 };
 
+struct AlwaysSupportsParachains;
+impl HeadSupportsParachains for AlwaysSupportsParachains {
+	fn head_supports_parachains(&self, _head: &Hash) -> bool { true }
+}
+
 struct Subsystem1;
 
 impl Subsystem1 {
@@ -146,6 +152,7 @@ fn main() {
 			vec![],
 			all_subsystems,
 			None,
+			AlwaysSupportsParachains,
 			spawner,
 		).unwrap();
 		let overseer_fut = overseer.run().fuse();