Fix: don't compare next_station when trying to merge CargoPackets

For vehicle packets they shouldn't be compared, and for station
packets they are already in a bucket per next_station.

src/cargopacket.h

@@ -422,7 +422,6 @@ public:
 		return cp1->source_xy == cp2->source_xy &&
 				cp1->periods_in_transit == cp2->periods_in_transit &&
 				cp1->source_type == cp2->source_type &&
-				cp1->next_station == cp2->next_station &&
 				cp1->source_id == cp2->source_id;
 	}
 };
@@ -537,7 +536,6 @@ public:
 		return cp1->source_xy == cp2->source_xy &&
 				cp1->periods_in_transit == cp2->periods_in_transit &&
 				cp1->source_type == cp2->source_type &&
-				cp1->next_station == cp2->next_station &&
 				cp1->source_id == cp2->source_id;
 	}
 };