Remove duo_workflow_in_ci Feature Flag

What does this MR do and why?

Removes feature flag duo_workflow_in_ci. This FF is default enabled and is not needed anymore. There should be no change in behavior for the Duo Agent Platform before / after this change, other than removing the ability to turn off the feature flag duo_workflow_in_ci

Notes:

• The feature flag was being pushed to the frontend, but I could not see any usage of duoWorkflowInCi
• Removed every check for duo_workflow_in_ci
• Removed test cases that checked a disabled duo_workflow_in_ci

Reference comment for removing the FF

References

Relates to https://gitlab.com/gitlab-org/gitlab/-/work_items/560928

How to set up and validate locally

1. Set up Duo Agent Platform
2. Test each Remote Flow
3. Check your Flow Output in Automate > Agent sessions
4. Run an Agentic Chat (web)
5. Run an Agentic Chat (IDE)

MR acceptance checklist

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