Unset BASE_URL for custom DNS deployment

We're not deployed at <http://agu2025.workshops.geojupyter.org/> so we
no longer need the BASE_URL that was useful when we were deployed at GH
Pages <https://geojupyter.github.io/workshop-open-source-geospatial>.

Author: mfisher87

.github/workflows/deploy-to-gh-pages.yml

@@ -5,9 +5,6 @@ on:
     branches: ["main"]
   workflow_dispatch:
 
-env:
-  BASE_URL: "/${{ github.event.repository.name }}"
-
 
 # Allow one concurrent deployment
 concurrency: