Remove CountUnrealized (#4357)

## Issue Addressed

Closes #4332

## Proposed Changes

Remove the `CountUnrealized` type, defaulting unrealized justification to _on_. This fixes the #4332 issue by ensuring that importing the same block to fork choice always results in the same outcome.

Finalized sync speed may be slightly impacted by this change, but that is deemed an acceptable trade-off until the optimisation from #4118 is implemented.

TODO:

- [x] Also check that the block isn't a duplicate before importing

beacon_node/network/src/sync/range_sync/chain.rs

@@ -3,7 +3,7 @@ use crate::beacon_processor::{ChainSegmentProcessId, WorkEvent as BeaconWorkEven
 use crate::sync::{
     manager::Id, network_context::SyncNetworkContext, BatchOperationOutcome, BatchProcessResult,
 };
-use beacon_chain::{BeaconChainTypes, CountUnrealized};
+use beacon_chain::BeaconChainTypes;
 use fnv::FnvHashMap;
 use lighthouse_network::{PeerAction, PeerId};
 use rand::seq::SliceRandom;
@@ -101,8 +101,6 @@ pub struct SyncingChain<T: BeaconChainTypes> {
     /// Batches validated by this chain.
     validated_batches: u64,
 
-    is_finalized_segment: bool,
-
     /// The chain's log.
     log: slog::Logger,
 }
@@ -128,7 +126,6 @@ impl<T: BeaconChainTypes> SyncingChain<T> {
         target_head_slot: Slot,
         target_head_root: Hash256,
         peer_id: PeerId,
-        is_finalized_segment: bool,
         log: &slog::Logger,
     ) -> Self {
         let mut peers = FnvHashMap::default();
@@ -150,7 +147,6 @@ impl<T: BeaconChainTypes> SyncingChain<T> {
             state: ChainSyncingState::Stopped,
             current_processing_batch: None,
             validated_batches: 0,
-            is_finalized_segment,
             log: log.new(o!("chain" => id)),
         }
     }
@@ -318,12 +314,7 @@ impl<T: BeaconChainTypes> SyncingChain<T> {
         // for removing chains and checking completion is in the callback.
 
         let blocks = batch.start_processing()?;
-        let count_unrealized = if self.is_finalized_segment {
-            CountUnrealized::False
-        } else {
-            CountUnrealized::True
-        };
-        let process_id = ChainSegmentProcessId::RangeBatchId(self.id, batch_id, count_unrealized);
+        let process_id = ChainSegmentProcessId::RangeBatchId(self.id, batch_id);
         self.current_processing_batch = Some(batch_id);
 
         if let Err(e) =