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.

common/eth2/src/lighthouse_vc/http_client.rs

@@ -57,7 +57,7 @@ pub fn parse_pubkey(secret: &str) -> Result<Option<PublicKey>, Error> {
         &secret[SECRET_PREFIX.len()..]
     };
 
-    eth2_serde_utils::hex::decode(secret)
+    serde_utils::hex::decode(secret)
         .map_err(|e| Error::InvalidSecret(format!("invalid hex: {:?}", e)))
         .and_then(|bytes| {
             if bytes.len() != PK_LEN {
@@ -174,7 +174,7 @@ impl ValidatorClientHttpClient {
         let message =
             Message::parse_slice(digest(&SHA256, &body).as_ref()).expect("sha256 is 32 bytes");
 
-        eth2_serde_utils::hex::decode(&sig)
+        serde_utils::hex::decode(&sig)
             .ok()
             .and_then(|bytes| {
                 let sig = Signature::parse_der(&bytes).ok()?;