Remove ultimate trials dependence on duo enterprise during applying

What does this MR do and why?

Remove ultimate trials dependence on duo enterprise during applying

• no longer required with DAP and so duo enterprise is not provisioned.
• Adjust text per https://gitlab.com/gitlab-org/gitlab/-/issues/585142#note_3035748082
• purge from our stubbing and rely on gitlab_subscription trial_ends_on instead for messaging and such
• see https://gitlab.com/gitlab-org/gitlab/-/work_items/585539
• see https://gitlab.com/gitlab-org/gitlab/-/work_items/585142

Screenshots or screen recordings

Before	After

How to set up and validate locally

Note: this area is fully covered by the feature specs.

The below only works if you have CDOT setup locally.

1. Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
2. In rails console enable the feature flag

   Feature.enable(:ultimate_trial_with_dap)

3. visit /-/trials/new path.
4. select a group or create one and apply.

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #585539