dictConfig in misc/greeter is excessive

It doesn't make sense to have the copy-pasted verbose logging configuration in `main.py`, `main_pingpong.py` and `main_pingpong_servicer.py`, which has the effect equal to

```python
logging.basicConfig(format="[%(asctime)s - %(name)s - %(levelname)s]:  %(message)s", level=logging.WARNING)
```