Cleanup duo enterprise rollout feature flags

What does this MR do and why?

Cleanup duo enterprise rollout feature flags

• feature rolled out successfully
• adjust a few missed areas where we need to convert 30 day to 60 day trial as well. There are some legacy trials that are still 30 days until 30 days from now, but those will go away too in the trial widget in 30 days via another effort for the trial widget.
• see https://gitlab.com/gitlab-org/gitlab/-/issues/500340

Changelog: other EE: true

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Related to #500340