rust/op-reth/crates/tests: justfile references non-existent paths

## Summary

The justfile (and Makefile before it) in `rust/op-reth/crates/tests/` references several paths that don't exist in the monorepo. These paths appear to be remnants from when op-reth was a standalone repository with its own submodules and directory structure.

Running `just` in this directory fails because the referenced paths are missing.

## Missing paths

All paths are relative to `rust/op-reth/crates/tests/`:

| Path | Referenced by |
|------|--------------|
| `../../../DockerfileOpProof` | `build-docker`, `build-docker-with-cov` |
| `proofs/contracts` | `build-contracts` |
| `proofs/core` | `test-e2e-sysgo` (default `GO_PKG_NAME`) |
| `optimism/op-deployer` | `update-packages` |
| `artifacts/compressed/artifacts.tzst` | `unzip-contract-artifacts` |

## Notes

- The `build` recipe works fine — `../../../` correctly resolves to the op-reth root and the Cargo manifest path is valid.
- This was broken before the just migration (the original Makefile had the same paths). The just migration in 0bcb263348 faithfully ported the broken targets.
- The README still references `make` commands and doesn't reflect the just migration either.

## Suggested fix

Either:
1. Update the paths to point to the correct locations in the monorepo, or
2. Remove the broken recipes if these test workflows are no longer used post-monorepo-integration

Start in rust/op-reth/crates/tests/Justfile and compare each listed recipe with the monorepo tree and the README's current commands. Check whether valid replacements exist for the Dockerfile, proofs, op-deployer, and artifact paths; done means `just` no longer references missing paths, or obsolete recipes are removed and the README matches the available commands.

Written by the indexing model from the issue text.