job.c: we need to remove the repeated getting time-at-creation in function cupsdLoadJob

[hustliyilin]

Obviously, https://github.com/apple/cups/blob/master/scheduler/job.c#L1701 and https://github.com/apple/cups/blob/master/scheduler/job.c#L1720 are repeated to get the time-at-creation, so we need to remove the repeated getting time-at-creation in function cupsdLoadJob.