chore(l1): remove total_difficulty

[JulianVentura]

Description

This PR fully removes total_difficulty field, as already done on #307, but later reverted on #566.
While doing so, it also removes the total_difficulty_check function, so it solves #790

Closes #790

[github-actions]

| File                                                                       | Lines | Diff |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/blockchain/fork_choice.rs           | 139   | -40  |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/api.rs                | 195   | -12  |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/rlp.rs                | 88    | -2   |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/store.rs              | 1247  | -25  |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/store_db/in_memory.rs | 481   | -35  |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/store_db/libmdbx.rs   | 890   | -37  |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/store_db/redb.rs      | 873   | -45  |
+----------------------------------------------------------------------------+-------+------+
| /home/runner/work/ethrex/ethrex/crates/storage/store/utils.rs              | 52    | -4   |
+----------------------------------------------------------------------------+-------+------+

Total lines added: 0
Total lines removed: 200
Total lines changed: 200

[mpaulucci]

Blocking this until we're sure it doesn't bring any regressions.

In mainnet this could be an issue since we have to deal with pre merge blocks.

[mpaulucci]

Switching the approach on this. Let's merge it, and if we find an issue, we can revert it.