ci: remove stale Flutter workflow

.github/workflows/flutter.yml

@@ -1,38 +0,0 @@
-name: Flutter CI
-
-on:
-  push:
-    branches: [ "main" ]
-  pull_request:
-    branches: [ "main" ]
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v3
-
-    - name: Set up Java
-      uses: actions/setup-java@v3
-      with:
-        distribution: 'zulu'
-        java-version: '17'
-
-    - name: Set up Flutter
-      uses: subosito/flutter-action@v2
-      with:
-        flutter-version: '3.19.x'
-        channel: 'stable'
-
-    - name: Get dependencies
-      run: flutter pub get
-
-    - name: Analyze code
-      run: flutter analyze
-
-    - name: Run tests
-      run: flutter test
-
-    - name: Build APK
-      run: flutter build apk --debug