Remove nightly workflow

.github/workflows/nightly.yml

-name: Nightly
-on:
-  schedule:
-    - cron: "0 0 * * *"
-
-jobs:
-  build_and_publish:
-    name: Build source distribution
-    if: github.repository == 'pymc-devs/pytensor'
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-        with:
-          fetch-depth: 0
-      - uses: actions/setup-python@v4
-        with:
-          python-version: "3.9"
-      - name: Install dependencies
-        run: |
-          python -m pip install -U pip
-          python -m pip install build
-      - name: Build the sdist
-        run: python -m build --sdist .
-        env:
-          BUILD_PYTENSOR_NIGHTLY: true
-      - uses: pypa/gh-action-pypi-publish@v1.8.4
-        with:
-          user: __token__
-          password: ${{ secrets.nightly_pypi_secret }}