Remove requirements.txt file

That file cannot distinguish required from optional dependencies, or alternative dependencies, so only serves to confuse things.

Author: chennes

.github/workflows/qt6-tests.yml

@@ -59,7 +59,7 @@ jobs:
       - name: Install Python dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install -r requirements.txt || true
+          pip install PySide6 vermin || true
 
       - name: Run App tests
         run: |