Remove create group option from duo pro trials

What does this MR do and why?

Remove create group option from duo pro trials

• it is not valid for free groups to create a duo pro trial, so it should be removed as an option since by default, newly created groups are free.
• change wording on page to indicate creating a group isn't an option
• see https://gitlab.com/gitlab-org/gitlab/-/issues/451776
• see note about guarding the duo pro page from allowing entry if no eligible groups in https://gitlab.com/gitlab-org/gitlab/-/issues/451776#note_1830942993
• also feature specs are coming see - https://gitlab.com/gitlab-org/gitlab/-/issues/451776#note_1830831787

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Before	After

How to set up and validate locally

bin/rails c

Feature.enable(:duo_pro_trials)

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
• Sign in. Create 2 groups following the below method...

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'ultimate'))

• Create group.

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'ultimate_trial'), trial_starts_on: 1.days.ago, trial_ends_on: 29.days.from_now, trial: true)

• Visit /-/trials/duo_pro/new?step=trial
• Make sure no create group option exists.

Related to #451776