docs: remove GitHub Action since unused

.github/workflows/docs.yml

@@ -1,18 +0,0 @@
-name: "Docs"
-on: [push, pull_request]
-
-jobs:
-  docs:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-      - uses: sphinx-toolbox/sphinx-action@master
-        with:
-          pre-build-command: "pip install .[docs]"
-          docs-folder: "docs/"
-      - name: Deploy
-        uses: peaceiris/actions-gh-pages@v3
-        if: github.ref == 'refs/heads/main'
-        with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: docs/_build/html