Remove trial column observance from the eligible trial query

What does this MR do and why?

Remove trial column observance from the eligible trial query

• CDOT does not change this to false/nil on downgrade, so we need to remove this condition, else premium or free namespaces that want to trial and had a legacy trial already will not be able to apply for a trial. internal slack for more info and previous MR work in !170327 (merged)
• see https://gitlab.com/gitlab-org/gitlab/-/issues/500325

Changelog: other EE: true

DB analysis

• eligible_for_trial - https://console.postgres.ai/gitlab/gitlab-production-main/sessions/33094/commands/102125
• ee/app/finders/users/trial_eligible_namespaces_finder.rb - https://console.postgres.ai/gitlab/gitlab-production-main/sessions/33094/commands/102127

MR acceptance checklist

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Related to #500325