Resolve "`ADM_update_job()` should only allow changing the job resources"

This MR removes the ADM_job_requirements argument from ADM_update_job. By design, job requirements can only be defined when the job submission occurs which means that, as of today, they cannot be changed dynamically. Thus, it doesn't make sense to be able to change them and removing the argument simplifies the daemon.

Closes #89 (closed)