Remove device lookup by name or number

[farmio]

xknx/xknx/devices/devices.py

Line 62 in 6ae7f3d

def __getitem__(self, key: str | int) -> Device:

await xknx.devices["TestOutlet"].set_on()
would only work as long as devices name attributes are unique - which we don't check anywhere.
Lookup by number doesn't have any real use imho.

I think it would be ok to remove this functionality in the future as it is safer for an application using it to just keep a reference to the object.
If anyone has objections, please let us know.