Move Vehicle Command Result Enum defs to Vehicle Command Ack (#19729)

- As it is always only used for the vehicle command ack message
- It was a duplicate, hence making it error prone for maintainment
- The uORB message comments were updated to make the relationship with
the MAVLink message / enum definitions clear

src/drivers/px4io/px4io.cpp

@@ -590,10 +590,10 @@ void PX4IO::Run()
 
 				/* publish ACK */
 				if (dsm_ret == OK) {
-					answer_command(cmd, vehicle_command_s::VEHICLE_CMD_RESULT_ACCEPTED);
+					answer_command(cmd, vehicle_command_ack_s::VEHICLE_CMD_RESULT_ACCEPTED);
 
 				} else {
-					answer_command(cmd, vehicle_command_s::VEHICLE_CMD_RESULT_FAILED);
+					answer_command(cmd, vehicle_command_ack_s::VEHICLE_CMD_RESULT_FAILED);
 				}
 			}
 		}