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/src/canonical_head.rs

@@ -45,8 +45,7 @@ use crate::{
 };
 use eth2::types::{EventKind, SseChainReorg, SseFinalizedCheckpoint, SseHead, SseLateHead};
 use fork_choice::{
-    CountUnrealizedFull, ExecutionStatus, ForkChoiceView, ForkchoiceUpdateParameters, ProtoBlock,
-    ResetPayloadStatuses,
+    ExecutionStatus, ForkChoiceView, ForkchoiceUpdateParameters, ProtoBlock, ResetPayloadStatuses,
 };
 use itertools::process_results;
 use parking_lot::{Mutex, RwLock, RwLockReadGuard, RwLockWriteGuard};
@@ -285,19 +284,13 @@ impl<T: BeaconChainTypes> CanonicalHead<T> {
         // defensive programming.
         mut fork_choice_write_lock: RwLockWriteGuard<BeaconForkChoice<T>>,
         reset_payload_statuses: ResetPayloadStatuses,
-        count_unrealized_full: CountUnrealizedFull,
         store: &BeaconStore<T>,
         spec: &ChainSpec,
         log: &Logger,
     ) -> Result<(), Error> {
-        let fork_choice = <BeaconChain<T>>::load_fork_choice(
-            store.clone(),
-            reset_payload_statuses,
-            count_unrealized_full,
-            spec,
-            log,
-        )?
-        .ok_or(Error::MissingPersistedForkChoice)?;
+        let fork_choice =
+            <BeaconChain<T>>::load_fork_choice(store.clone(), reset_payload_statuses, spec, log)?
+                .ok_or(Error::MissingPersistedForkChoice)?;
         let fork_choice_view = fork_choice.cached_fork_choice_view();
         let beacon_block_root = fork_choice_view.head_block_root;
         let beacon_block = store