Remove unused validated_user_levels table

[jmkulwik]

Initial creation of the user_level_info table: #31429
Rename of user_level_info to validated_user_levels: #31731

We want to start tracking the time students spend on levels. To do this, we wanted to add a time_spent column to the user_levels table. Since the user_levels table has more than 2 billion entries, we decided to try alternate approaches. Using a referential validated_user_levels table was one of these alternate approaches. However, we decided not to follow through on this approach and are instead going to investigate ways we can add the time_spent column directly to the user_levels table.

New attempt to add time_spent to the user_levels table: #36082

The validated_user_levels table has no entries on production or test and only a few entries on staging.

Links

Testing story

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked