remove protocol from PushBotEthernetDevice

[Christian-B]

The class PushBotEthernetDevice has a setter and getter for a "protocol"

However the two "protocol" classes are so different they do not even share a common API.

So it does not make sense to story this at the Abstract level.

As the Set and Get would have to be typed "Any"

[Christian-B]

On farther examination the "protocol" is always a MunichIoSpiNNakerLinkProtocol in contrast to what the docs claim.

MunichIoEthernetProtocol is actually just a utils class

[Christian-B]

Will fix in the overrides pr