Remove cancel method from ReservationManager (open-rmf#483)

Removed the cancel method from ReservationManager as this is not implemented and was removed in open-rmf#416 

Thanks @cwrx777 for highlighting this error in open-rmf#482

Signed-off-by: Arjo Chakravarty <arjoc@intrinsic.ai>
Co-authored-by: Grey <greyxmike@gmail.com>

Author: arjo129

rmf_fleet_adapter/src/rmf_fleet_adapter/agv/ReservationManager.hpp

@@ -33,9 +33,6 @@ class ReservationManager
   void replace_ticket(
     const rmf_reservation_msgs::msg::ReservationAllocation new_allocation);
 
-  /// Cancels the current reservation
-  void cancel();
-
   /// Retrieves the location name of the current reservation. Returns empty string if
   /// no location is found.
   std::string get_reserved_location() const;