Fork choice modifications and cleanup (#3962)

## Issue Addressed

NA

## Proposed Changes

- Implements https://github.com/ethereum/consensus-specs/pull/3290/
- Bumps `ef-tests` to [v1.3.0-rc.4](https://github.com/ethereum/consensus-spec-tests/releases/tag/v1.3.0-rc.4).

The `CountRealizedFull` concept has been removed and the `--count-unrealized-full` and `--count-unrealized` BN flags now do nothing but log a `WARN` when used.

## Database Migration Debt

This PR removes the `best_justified_checkpoint` from fork choice. This field is persisted on-disk and the correct way to go about this would be to make a DB migration to remove the field. However, in this PR I've simply stubbed out the value with a junk value. I've taken this approach because if we're going to do a DB migration I'd love to remove the `Option`s around the justified and finalized checkpoints on `ProtoNode` whilst we're at it. Those options were added in #2822 which was included in Lighthouse v2.1.0. The options were only put there to handle the migration and they've been set to `Some` ever since v2.1.0. There's no reason to keep them as options anymore.

I started adding the DB migration to this branch but I started to feel like I was bloating this rather critical PR with nice-to-haves. I've kept the partially-complete migration [over in my repo](https://github.com/paulhauner/lighthouse/tree/fc-pr-18-migration) so we can pick it up after this PR is merged.

consensus/proto_array/src/fork_choice_test_definition.rs

@@ -3,7 +3,6 @@ mod ffg_updates;
 mod no_votes;
 mod votes;
 
-use crate::proto_array::CountUnrealizedFull;
 use crate::proto_array_fork_choice::{Block, ExecutionStatus, ProtoArrayForkChoice};
 use crate::{InvalidationOperation, JustifiedBalances};
 use serde_derive::{Deserialize, Serialize};
@@ -88,7 +87,6 @@ impl ForkChoiceTestDefinition {
             junk_shuffling_id.clone(),
             junk_shuffling_id,
             ExecutionStatus::Optimistic(ExecutionBlockHash::zero()),
-            CountUnrealizedFull::default(),
         )
         .expect("should create fork choice struct");
         let equivocating_indices = BTreeSet::new();
@@ -307,8 +305,8 @@ fn get_checkpoint(i: u64) -> Checkpoint {
 
 fn check_bytes_round_trip(original: &ProtoArrayForkChoice) {
     let bytes = original.as_bytes();
-    let decoded = ProtoArrayForkChoice::from_bytes(&bytes, CountUnrealizedFull::default())
-        .expect("fork choice should decode from bytes");
+    let decoded =
+        ProtoArrayForkChoice::from_bytes(&bytes).expect("fork choice should decode from bytes");
     assert!(
         *original == decoded,
         "fork choice should encode and decode without change"