Centralize robots.txt and sitemap

- One robots.txt at root referencing two sitemaps
- One central sitemap.xml with all pages (no per-site sitemaps)
- Deleted: 4 per-site sitemap templates, 4 per-site robots.txt files
- Simplified sitemap template (uses collections.all)

hub/robots.txt

@@ -2,8 +2,4 @@ User-agent: *
 Allow: /
 
 Sitemap: https://www.moonweb.org/sitemap.xml
-Sitemap: https://www.moonweb.org/infra/sitemap.xml
-Sitemap: https://www.moonweb.org/smarthome/sitemap.xml
-Sitemap: https://www.moonweb.org/code/sitemap.xml
-Sitemap: https://www.moonweb.org/retro/sitemap.xml
 Sitemap: https://www.moonweb.org/timecapsule/sitemap.xml

hub/sitemap.xml.njk

@@ -1,6 +1,5 @@
 ---
 permalink: /sitemap.xml
-sitemapCollection: "hub"
 eleventyExcludeFromCollections: true
 ---
 {% include "sitemap.njk" %}