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/lib.rs

@@ -52,8 +52,8 @@ pub mod validator_pubkey_cache;
 
 pub use self::beacon_chain::{
     AttestationProcessingOutcome, BeaconChain, BeaconChainTypes, BeaconStore, ChainSegmentResult,
-    CountUnrealized, ForkChoiceError, OverrideForkchoiceUpdate, ProduceBlockVerification,
-    StateSkipConfig, WhenSlotSkipped, INVALID_FINALIZED_MERGE_TRANSITION_BLOCK_SHUTDOWN_REASON,
+    ForkChoiceError, OverrideForkchoiceUpdate, ProduceBlockVerification, StateSkipConfig,
+    WhenSlotSkipped, INVALID_FINALIZED_MERGE_TRANSITION_BLOCK_SHUTDOWN_REASON,
     INVALID_JUSTIFIED_PAYLOAD_SHUTDOWN_REASON, MAXIMUM_GOSSIP_CLOCK_DISPARITY,
 };
 pub use self::beacon_snapshot::BeaconSnapshot;
@@ -64,6 +64,7 @@ pub use attestation_verification::Error as AttestationError;
 pub use beacon_fork_choice_store::{BeaconForkChoiceStore, Error as ForkChoiceStoreError};
 pub use block_verification::{
     get_block_root, BlockError, ExecutionPayloadError, GossipVerifiedBlock,
+    IntoExecutionPendingBlock,
 };
 pub use canonical_head::{CachedHead, CanonicalHead, CanonicalHeadRwLock};
 pub use eth1_chain::{Eth1Chain, Eth1ChainBackend};