Remove deprecated styles

What does this MR do and why?

This removes some style overrides that have been moved to GitLab UI.

Screenshots or screen recordings

How to set up and validate locally

Taken from !64540 (diffs):

1. Enable billing plans & trials:

   ApplicationSetting.first.update(check_namespace_plan: true)

2. Enable the feature flag for this experiment:

   Feature.enable_percentage_of_time(:show_trial_status_in_sidebar, 100)

3. Grab a group you like to use locally, get its id, and then give that group a trial:

   group = Group.find(<group_id>)
   plan = Plan.create_with(title: 'Ultimate').find_or_create_by(name: 'ultimate')
   days_remaining_in_trial = 14
   subscription = group.gitlab_subscription || GitlabSubscription.new(namespace: group)
   subscription.hosted_plan = plan
   subscription.trial_starts_on = Date.current.advance(days: days_remaining_in_trial - 30)
   subscription.trial_ends_on = Date.current.advance(days: days_remaining_in_trial)
   subscription.trial = true
   subscription.save
   
   # then you should see...
   group.reload.trial_active? # => true

4. Then navigate to that group in the UI.

5. You can also play around with how many days are left in the group’s trial:

   group = Group.find(<group_id>)
   days_remaining_in_trial = 3
   group.gitlab_subscription.update(
     trial_starts_on: Date.current.advance(days: days_remaining_in_trial - 30),
     trial_ends_on: Date.current.advance(days: days_remaining_in_trial)
   )

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.