This allows jobs to be deleted from the database.
Currently only implemented by fsjobqueue. The function for
dbjobqueue currently returns nil.
This will remove all the job files used by the root job UUID as long as
no other job depends on them. ie. It starts at the top, and moves down
the dependency tree until it finds a job that is also used by another
job, removes the job to be deleted from its dependants list, and moves
back up the tree only deleting jobs with empty dependants lists.
Related: RHEL-60120
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