Clean up experiment flag code

[kpamaran]

refactor(indexes): remove expired index guidance experiment code NAT-7

Description

Removed all code related to the "Early Journey Indexes Guidance & Awareness" experiment (CLOUDP-239367), which concluded in March 2025.

Key changes include:

• Deletion of experiment-specific UI components (e.g., index-flow-section, query-flow-section, create-index-modal-header, mdb-code-viewer).
• Removal of enableIndexesGuidanceExp and showIndexesGuidanceVariant feature flags.
• Removal of earlyJourneyIndexesGuidance telemetry enum.
• Simplification of create-index-modal.tsx and create-index-form.tsx by removing conditional rendering and experiment-specific props.
• Cleanup of create-index.tsx and create-index-actions.tsx to remove experiment-related state, actions, and logic.
• Deletion of useEffect in entrypoint.tsx for saving experiment preferences.
• Updates to relevant tests to remove experiment-specific cases.

This cleanup reverts the create index functionality to its non-experiment state.

Checklist

• New tests and/or benchmarks are included
• Documentation is changed or added
• If this change updates the UI, screenshots/videos are added and a design review is requested
• I have signed the MongoDB Contributor License Agreement (https://www.mongodb.com/legal/contributor-agreement)

Motivation and Context

This change removes expired experiment code, reducing technical debt and simplifying the codebase.

• Bugfix
• New feature
• Dependency update
• Misc

Open Questions

Dependents

Types of changes

• Backport Needed
• Patch (non-breaking change which fixes an issue)
• Minor (non-breaking change which adds functionality)
• Major (fix or feature that would cause existing functionality to change)

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Linear Issue: NAT-7

 

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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