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/beacon_chain/src/fork_revert.rs

@@ -1,5 +1,5 @@
 use crate::{BeaconForkChoiceStore, BeaconSnapshot};
-use fork_choice::{CountUnrealized, ForkChoice, PayloadVerificationStatus};
+use fork_choice::{ForkChoice, PayloadVerificationStatus};
 use itertools::process_results;
 use slog::{info, warn, Logger};
 use state_processing::state_advance::complete_state_advance;
@@ -100,7 +100,6 @@ pub fn reset_fork_choice_to_finalization<E: EthSpec, Hot: ItemStore<E>, Cold: It
     store: Arc<HotColdDB<E, Hot, Cold>>,
     current_slot: Option<Slot>,
     spec: &ChainSpec,
-    count_unrealized_config: CountUnrealized,
 ) -> Result<ForkChoice<BeaconForkChoiceStore<E, Hot, Cold>, E>, String> {
     // Fetch finalized block.
     let finalized_checkpoint = head_state.finalized_checkpoint();
@@ -166,8 +165,7 @@ pub fn reset_fork_choice_to_finalization<E: EthSpec, Hot: ItemStore<E>, Cold: It
         .map_err(|e| format!("Error loading blocks to replay for fork choice: {:?}", e))?;
 
     let mut state = finalized_snapshot.beacon_state;
-    let blocks_len = blocks.len();
-    for (i, block) in blocks.into_iter().enumerate() {
+    for block in blocks {
         complete_state_advance(&mut state, None, block.slot(), spec)
             .map_err(|e| format!("State advance failed: {:?}", e))?;
 
@@ -190,15 +188,6 @@ pub fn reset_fork_choice_to_finalization<E: EthSpec, Hot: ItemStore<E>, Cold: It
         // This scenario is so rare that it seems OK to double-verify some blocks.
         let payload_verification_status = PayloadVerificationStatus::Optimistic;
 
-        // Because we are replaying a single chain of blocks, we only need to calculate unrealized
-        // justification for the last block in the chain.
-        let is_last_block = i + 1 == blocks_len;
-        let count_unrealized = if is_last_block {
-            count_unrealized_config
-        } else {
-            CountUnrealized::False
-        };
-
         fork_choice
             .on_block(
                 block.slot(),
@@ -209,7 +198,6 @@ pub fn reset_fork_choice_to_finalization<E: EthSpec, Hot: ItemStore<E>, Cold: It
                 &state,
                 payload_verification_status,
                 spec,
-                count_unrealized,
             )
             .map_err(|e| format!("Error applying replayed block to fork choice: {:?}", e))?;
     }