Remove old unused CI

I'm never going to finish that rework anyway

.github/workflows/2019.yml

@@ -1,18 +0,0 @@
-name: AOC 2019 test suite
-on:
-  push:
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-python@v2
-        with:
-          python-version: 3.9
-      - name: Install dependencies
-        run: |
-          python -m pip install --upgrade pip
-          pip install -r 2019/requirements.txt
-      - name: Run Pytest
-        run: pytest 2019