Clean up code and delete the `Attempt` table

[faucomte97]

Finally, we will be able amend the code so that retrieving scores only reads from the LevelMetrics table.
And we will be able to delete the Attempt table for good.

---

🔗 Learn how to work on this issue.
🔗 Visit our site.
🔗 Read our docs.
🔗 Read our code.
🔗 Learn how to format text on GitHub.