run autoflake

```
autoflake -i --remove-unused-variables $(find . -name "*.py")
```

lnbits/tasks.py

@@ -3,7 +3,7 @@ import time
 import traceback
 import uuid
 from http import HTTPStatus
-from typing import Callable, Dict, List
+from typing import Dict
 
 from fastapi.exceptions import HTTPException
 from loguru import logger