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>

testing/ef_tests/src/cases/common.rs

@@ -1,4 +1,4 @@
-use serde_derive::Deserialize;
+use serde::Deserialize;
 use ssz::Encode;
 use ssz_derive::{Decode, Encode};
 use std::convert::TryFrom;