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/Cargo.toml

@@ -13,7 +13,7 @@ tokio = { version = "1.14.0", features = ["time", "rt-multi-thread", "macros"] }
 logging = { path = "../common/logging" }
 
 [dependencies]
-tree_hash = "0.4.1"
+tree_hash = "0.5.0"
 clap = "2.33.3"
 slashing_protection = { path = "./slashing_protection" }
 slot_clock = { path = "../common/slot_clock" }
@@ -46,7 +46,7 @@ lighthouse_version = { path = "../common/lighthouse_version" }
 warp_utils = { path = "../common/warp_utils" }
 warp = "0.3.2"
 hyper = "0.14.4"
-eth2_serde_utils = "0.1.1"
+ethereum_serde_utils = "0.5.0"
 libsecp256k1 = "0.7.0"
 ring = "0.16.19"
 rand = { version = "0.8.5", features = ["small_rng"] }