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.

beacon_node/beacon_chain/tests/tests.rs

@@ -500,7 +500,7 @@ async fn unaggregated_attestations_added_to_fork_choice_some_none() {
     // Move forward a slot so all queued attestations can be processed.
     harness.advance_slot();
     fork_choice
-        .update_time(harness.chain.slot().unwrap(), &harness.chain.spec)
+        .update_time(harness.chain.slot().unwrap())
         .unwrap();
 
     let validator_slots: Vec<(usize, Slot)> = (0..VALIDATOR_COUNT)
@@ -614,7 +614,7 @@ async fn unaggregated_attestations_added_to_fork_choice_all_updated() {
     // Move forward a slot so all queued attestations can be processed.
     harness.advance_slot();
     fork_choice
-        .update_time(harness.chain.slot().unwrap(), &harness.chain.spec)
+        .update_time(harness.chain.slot().unwrap())
         .unwrap();
 
     let validators: Vec<usize> = (0..VALIDATOR_COUNT).collect();