Remove serde derive references (#4830)

* remove remaining uses of serde_derive

* fix lockfile

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

common/eth2_interop_keypairs/src/lib.rs

@@ -22,7 +22,7 @@ extern crate lazy_static;
 use bls::{Keypair, PublicKey, SecretKey};
 use ethereum_hashing::hash;
 use num_bigint::BigUint;
-use serde_derive::{Deserialize, Serialize};
+use serde::{Deserialize, Serialize};
 use std::convert::TryInto;
 use std::fs::File;
 use std::path::PathBuf;