Remove serde derive references (#4830)

* remove remaining uses of serde_derive

* fix lockfile

---------

Co-authored-by: João Oliveira <hello@jxs.pt>

validator_client/src/config.rs

@@ -8,7 +8,7 @@ use directory::{
 };
 use eth2::types::Graffiti;
 use sensitive_url::SensitiveUrl;
-use serde_derive::{Deserialize, Serialize};
+use serde::{Deserialize, Serialize};
 use slog::{info, warn, Logger};
 use std::fs;
 use std::net::IpAddr;

validator_client/src/graffiti_file.rs

@@ -1,4 +1,4 @@
-use serde_derive::{Deserialize, Serialize};
+use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 use std::fs::File;
 use std::io::{prelude::*, BufReader};