Update Docsy and drop blog layout overrides

[chalin]

• Blog index pages now have titles and breadcrumbs.
• Contributes to Blog updates and enhancements 25Q1 #5902
• Drops blog-layout overrides that are no longer necessary
• Drops td-breadcrumbs__single style override that is no longer necessary.
• No other changes to generated site files other than whitespace cleanup:

$ (cd public && git diff -bw --ignore-blank-lines) | grep ^diff | grep -v /index.html 
diff --git a/scss/main.css b/scss/main.css
diff --git a/scss/main.css.map b/scss/main.css.map

Previews:

• https://deploy-preview-5915--opentelemetry.netlify.app/docs/ - notice that breadcrumb is still hidden
• Notice how the title and breadcrumbs are shown:
  • https://deploy-preview-5915--opentelemetry.netlify.app/blog/
  • https://deploy-preview-5915--opentelemetry.netlify.app/blog/2024/
  • https://deploy-preview-5915--opentelemetry.netlify.app/blog/2025/ -- also shows "Happy new year" index-page content
  • https://deploy-preview-5915--opentelemetry.netlify.app/blog/page/15/