fix(ci): remove sitemap entry from generated robots.txt

Agent-Logs-Url: https://github.com/nextcloud/documentation/sessions/0af863bf-06c5-4928-81ea-59ff95c2e85a

Co-authored-by: skjnldsv <14975046+skjnldsv@users.noreply.github.com>

Author: 2 people

.github/workflows/sphinxbuild.yml

@@ -520,7 +520,6 @@ jobs:
           # Only the stable version should be indexed
           Allow: /server/stable/
           Disallow: /server/
-          Sitemap: https://docs.nextcloud.com/sitemap.xml
           EOF
 
         # Remove the stage/ directory BEFORE creating the PR so it doesn't get committed