[TC-128] Job tables - remove unused tables from TO

[limited]

The following job tables are not used and should probably be removed as well as the code that depends on them:

• job_agent
• job_status
• job_result

the only job table that needs to stay is:

• job

and maybe it should be renamed to "revalidate_job" as the only type of job that is ever created is a revalidate (invalidate content) job.

Author: Jeremy Mitchell
JIRA Link: https://issues.apache.org/jira/browse/TC-128

[rawlinp]

@TaylorCFrey -- just for awareness. I think you're planning to remove these tables as part of the REFETCH/REFRESH invalidation project, so we can close this out once that's done.