Remove departureTime from Carpool

[frankgerhardt]

Remove departureTime from Carpool, because it's a duplicate of the departureTime of the first Stop.
If both are in the schema, then both must have the same values which might not be the case always or needs extra work to enforce and check. They could be different, one of them could be null. What then? What has precendence? If there is only one departureTime there can not be any confusion. And there is always a first Stop where the time can be taken from.