Fix: Duo Flows Setting Disabled shows checkbox

What does this MR do and why?

Remove the extra checkbox that displays on the Flows settings when Duo is set to Always off.

References

GitLab Issue: #577538 (closed)

Screenshots or screen recordings

Before	After

Screen Recording
Screen_Recording_2025-10-21_at_7.29.19_PM

How to set up and validate locally

To Test Locally

1. Turn on the following feature flags: duo_workflow.
2. Also make sure you have Duo Settings configured and you are running in SaaS (see local Duo set-up here). Make sure Duo is available for the group you are testing.
3. Go to your [Group] > Settings > GitLab Duo settings.
4. Select Change configuration.
5. Select Always off under GitLab Duo availability, notice that the checkbox no longer appears next to the freshly disabled Allow flow execution checkbox.
6. Click Save changes to update.
7. Go to a subgroup of the group that you are in.
8. Go to the settings via Settings > General,
9. Validate under GitLab Duo features that Allow flow execution is disabled and that no checkbox also appears.

MR acceptance checklist

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Related to #577538 (closed)