Removing outdated Polaris reference docs

Polaris reference docs now follow the same versioning policy as Shopify's GraphQL APIs: Each stable version is supported for a minimum of 12 months. Older versions continue to work, they just won’t have dedicated docs on Shopify.dev. Shopify CLI already prevents deploys targeting API versions older than 12 months, so we recommend keeping your extensions on a supported version.

Starting with the 2026-04 release, we'll only publish docs for the last four stable versions of these reference docs:

• Admin UI extensions
• Checkout UI extensions
• Customer account UI extensions
• POS UI extensions