Remove non-super sidebar trial status widget code

What does this MR do and why?

Remove non-super sidebar trial status widget code

• no longer needed since super sidebar is fully cut over
• trial status widget is instead invoked for super sidebar through the sidebars helper.
• feature specs that cover this showing up in sidebar correctly: ee/spec/features/trials/trial_widget_in_sidebar_spec.rb
• see #458815 (closed)

MR acceptance checklist

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Screenshots or screen recordings

no change

How to set up and validate locally

1. Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
2. create a group
3. In the gitlab admin UI, edit the group to be on an ultimate trial
4. In rails console, change the trial, trial start and end date for the group

   Group.last.gitlab_subscription.update_columns(trial_starts_on: Date.today, trial_ends_on: 30.days.from_now, trial: true)

5. Go to group overview page and check super sidebar and ensure status widget appears.

Related to #458815 (closed)