Cleanup the flattening / unflattening logic

[akolson]

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Overview

This is a follow-up task to clean up the flattening/unflattening logic currently implemented on the search recommendation UI in Studio.

Description and outcomes

• We are currently using these functions to flatten and unflatten responses received from the recommender API.
• We should instead refactor this to use the models/querysets instead.

Acceptance Criteria

• The refactor doesn't introduce any regressions

Assumptions and Dependencies

• NA

Accessibility Requirements

• NA

Resources

• Search and folder contextualized content recommendations #4044