Remove ADP availability admonition for GA descope

[micheleRP]

Summary

Drops the page.attributes.adp availability block from src/partials/article.hbs. ADP Cloud is descoped from the 2026-06-15 GA, so BYOC is the only deployment shape and the "Available in: Cloud, BYOC" / "Available in: BYOC" admonition that the bundle injects on every ADP page no longer informs the reader.

The block was added in 37bacc1 ("Add availability block and enhance ADP page styling") and refined in 5b36bdd ("Address CodeRabbit review comments"). This PR removes it entirely now that the descope decision has landed.

Other badges keep working unchanged: beta, limited-availability, context-switcher, and the BYOC / Cloud nav-metadata labels for non-ADP pages (lines 32-43 are untouched, still gated on {{#unless page.attributes.adp}}).

Companion PR

redpanda-data/adp-docs#13 ships the same change locally as an Antora supplemental_files override so the deploy preview build is fixed immediately, ahead of a docs-ui release. Once this PR merges, a new release tag is cut from feature/badge-byoc-only, and the adp-docs / docs-site playbooks are bumped to the new release, the supplemental-ui/ override in adp-docs becomes redundant and can be deleted (cleanup PR will follow).

Test plan

• gulp lint passes cleanly (CSS + JS).
• After release: adp-docs build with the new bundle no longer renders any <div class="availability-block"> on ADP pages.
• After release: non-ADP pages still get the BYOC / Cloud nav badges where applicable.
• After release: beta and limited-availability badges still render correctly.

🤖 Generated with Claude Code

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