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.

validator_client/src/http_api/tests.rs

@@ -365,7 +365,7 @@ impl ApiTester {
             let withdrawal_keypair = keypairs.withdrawal.decrypt_keypair(PASSWORD_BYTES).unwrap();
 
             let deposit_bytes =
-                eth2_serde_utils::hex::decode(&response[i].eth1_deposit_tx_data).unwrap();
+                serde_utils::hex::decode(&response[i].eth1_deposit_tx_data).unwrap();
 
             let (deposit_data, _) =
                 decode_eth1_tx_data(&deposit_bytes, E::default_spec().max_effective_balance)