Remove LC server config from HTTP API (#7017)

Partly addresses

- https://github.com/sigp/lighthouse/issues/6959


  Use the `enable_light_client_server` field from the beacon chain config in the HTTP API. I think we can make this the single source of truth, as I think the network crate also has access to the beacon chain config.

beacon_node/http_api/src/test_utils.rs

@@ -249,7 +249,6 @@ pub async fn create_api_server_with_config<T: BeaconChainTypes>(
             enabled: true,
             listen_port: port,
             data_dir: std::path::PathBuf::from(DEFAULT_ROOT_DIR),
-            enable_light_client_server: true,
             ..http_config
         },
         chain: Some(chain),