BI-2805 - Fix autocomplete to work with new BrAPI levelNames

[nickpalladino]

Description

Story: BI-2805

• Switched to use GET /programs/${programId}/experiments/${experimentId}/recommended-sub-entity-dataset-names endpoint
• Cleaned up unused imports
• Remove front-end filtering of dataset names already used in experiment as it is now done in the backend
• Left in front-end existing dataset name check on sub entity dataset creation

Dependencies

• bi-api feature/BI-2805

Testing

• See acceptance criteria in BI-2805

Checklist:

• I have performed a self-review of my own code
• I have tested my code and ensured it meets the acceptance criteria of the story
• I have commented my code, particularly in hard-to-understand areas
• I have either updated the source of truth or arranged for update with product owner if needed https://breedinginsight.atlassian.net/wiki/spaces/BI/pages/1559953409/Source+of+Truth
• I have run SiteImprove on pages impacted by changes