Removes a train from the model. There are two ways a train can be removed: it can move out of the rail yard via an open-ended track, in which case
should follow the last
block that was controlling the train, or it can "disappear" from any location in the rail yard, provided it is not moving.
Exit) must be used to remove any trains.
long count() - Returns the number of trains disposed by this TrainDispose.
The input port.