remove gordon bell guide now it is over (#240)

Author: bcumming

docs/guides/gb25.md

@@ -142,7 +142,6 @@ nav:
     - guides/index.md
     - 'Internet Access on Alps': guides/internet-access.md
     - 'Storage': guides/storage.md
-    - 'Gordon Bell 2025': guides/gb25.md
   - 'Policies':
     - policies/index.md
     - 'User Regulations': policies/regulations.md