Remove start and end link from route

[paulheinr]

In Java, start and end link are not part of the network route (i.e., link id sequence), even though they are part of the route description in the population xml file. This is in principle no problem -- as long as we don't get routes from an external service. For now, the external service needs to ensure that start and end link id are part of the network route. It would be cleaner, if Java and Rust interally behave the same. Therefore, Rust should also internally don't store start and end link in route link sequence.