Remove entries linking to defunct platforms and dead URLs

Prune resources hosted on platforms that no longer serve the original
content:
- javascriptair.com (defunct podcast network)
- scotch.io (acquired, old URLs broken)
- tutorialzine.com (domain sold, content gone)
- alligator.io (merged into DigitalOcean, old URLs dead)
- pusher.com/tutorials (5 entries, tutorial subdirectory removed)
- gold.xitu.io (migrated to juejin.cn)
- embalses.azurewebsites.net (expired Azure free-tier demo)
- openfunctioncomputers.com (Vue 1.x-era project, dead)
- YouTube AdBlitz 2016 (one-time campaign, domain decommissioned)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>