ContextDeserialize and Beacon API Improvements (#7372)

* #7286
* BeaconAPI is not returning a versioned response when it should for some V1 endpoints
* these [strange functions with vX in the name that still accept `endpoint_version` arguments](https://github.com/sigp/lighthouse/blob/stable/beacon_node/http_api/src/produce_block.rs#L192)

This refactor is a prerequisite to get the fulu EF tests running.

beacon_node/http_api/src/aggregate_attestation.rs

@@ -4,7 +4,7 @@ use crate::version::{add_consensus_version_header, V1, V2};
 use beacon_chain::{BeaconChain, BeaconChainTypes};
 use eth2::types::{self, EndpointVersion, Hash256, Slot};
 use std::sync::Arc;
-use types::fork_versioned_response::EmptyMetadata;
+use types::beacon_response::EmptyMetadata;
 use types::{CommitteeIndex, ForkVersionedResponse};
 use warp::{
     hyper::{Body, Response},
@@ -52,7 +52,7 @@ pub fn get_aggregate_attestation<T: BeaconChainTypes>(
 
     if endpoint_version == V2 {
         let fork_versioned_response = ForkVersionedResponse {
-            version: Some(fork_name),
+            version: fork_name,
             metadata: EmptyMetadata {},
             data: aggregate_attestation,
         };