Update product availability details for import docs

What does this MR do and why?

• Updates the product availability details for some of the import docs and removes duplicate information from subheadings
• Sets remove_date and redirect_to for a removed page
• Deletes links from https://docs.gitlab.com/ee/update/deprecations.html to the removed page

Related guidance

• https://docs.gitlab.com/ee/development/documentation/styleguide/availability_details.html#duplicating-tier-offering-or-status-on-subheadings
• https://docs.gitlab.com/ee/development/documentation/styleguide/deprecations_and_removals.html#remove-a-page

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