Fix duplicate key removal

Author: Ross-Sherlock

solutions/java/src/parkinglot/ParkingLot.java

@@ -69,7 +69,6 @@ public Optional<Double> unparkVehicle(String licenseNumber) {
 
         ticket.setExitTimestamp();
         ticket.getSpot().unparkVehicle();
-        activeTickets.remove(ticket.getTicketId());
 
         Double parkingFee = feeStrategy.calculateFee(ticket);