Remove Claude Sonnet 3.5 due to Anthropic deprecation and retirement

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Background

• claude-3-5-sonnet-20240620 is currently available as a selectable model within Duo. Anthropic deprecated the model on 2025-08-13 and will fully retire the model on 2025-10-22
  • https://docs.claude.com/en/docs/about-claude/model-deprecations#model-status
• claude-3-5-sonnet-20240620 is used within Duo but not currently within Duo Agent Platform.
  • gitlab-org/modelops/applied-ml/code-suggestions/ai-assist!3360 (merged)
• We've sent communications to customers who are currently using this model, and need to provide a specific date when the model will be removed from Duo. This will allow customers to plan to update to an alternate model via Model Selection.
• Prior Slack discussion: https://gitlab.slack.com/archives/C051K31F30R/p1758669689219259?thread_ts=1757681621.315629&cid=C051K31F30R

Proposal

• Remove claude-3-5-sonnet-20240620 from Duo on 2025-10-15 2025-10-08. This provides a few weeks for customers to make a change, and allows us 1 week ahead of the 2025-10-22 retirement date in case there any issues with the change.