chore: remove ai-search config

[sbawabe]

Summary

Removes the ai-search config block from fern/docs.yml as the team is moving away from this configuration. Per discussion in #project-docs-ftux.

# Removed:
ai-search:
  location:
    - docs

Review & Testing Checklist for Human

• Confirm that removing ai-search doesn't break the docs build (CI should validate this)
• Verify that search still works as expected on the deployed starter docs site after merge

Notes

A matching PR is being created for docs-starter-internal with the same change.

Link to Devin session: https://app.devin.ai/sessions/b569dcd0b47f4153a4ed85e0cc7f524a
Requested by: @sbawabe

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