Split common crates out into their own repos (#3890)

## Proposed Changes

Split out several crates which now exist in separate repos under `sigp`.

- [`ssz` and `ssz_derive`](https://github.com/sigp/ethereum_ssz)
- [`tree_hash` and `tree_hash_derive`](https://github.com/sigp/tree_hash)
- [`ethereum_hashing`](https://github.com/sigp/ethereum_hashing)
- [`ethereum_serde_utils`](https://github.com/sigp/ethereum_serde_utils)
- [`ssz_types`](https://github.com/sigp/ssz_types)

For the published crates see: https://crates.io/teams/github:sigp:crates-io?sort=recent-updates.

## Additional Info

- [x] Need to work out how to handle versioning. I was hoping to do 1.0 versions of several crates, but if they depend on `ethereum-types 0.x` that is not going to work. EDIT: decided to go with 0.5.x versions.
- [x] Need to port several changes from `tree-states`, `capella`, `eip4844` branches to the external repos.

crypto/bls/src/generic_public_key_bytes.rs

@@ -2,9 +2,9 @@ use crate::{
     generic_public_key::{GenericPublicKey, TPublicKey},
     Error, PUBLIC_KEY_BYTES_LEN,
 };
-use eth2_serde_utils::hex::encode as hex_encode;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
+use serde_utils::hex::encode as hex_encode;
 use ssz::{Decode, Encode};
 use std::convert::TryInto;
 use std::fmt;