Remove old workflow

.github/workflows/main.yml

@@ -1,34 +0,0 @@
-# Based on https://docs.platformio.org/en/latest/integration/ci/github-actions.html
-name: PlatformIO CI
-
-on: [push, pull_request]
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v2
-    - name: Cache pip
-      uses: actions/cache@v2
-      with:
-        path: ~/.cache/pip
-        key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
-        restore-keys: |
-          ${{ runner.os }}-pip-
-    - name: Cache PlatformIO
-      uses: actions/cache@v2
-      with:
-        path: ~/.platformio
-        key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}
-    - name: Set up Python
-      uses: actions/setup-python@v2
-    - name: Install PlatformIO
-      run: |
-        python -m pip install --upgrade pip
-        pip install --upgrade platformio
-
-    - name: Install library dependencies
-      run: pio lib -g install 1
-
-    - name: Run PlatformIO
-      run: pio ci --project-conf platformio.ini .