Bug 30181: (follow-up) Remove redundant queries and parameters

Bug 30181: (follow-up) Remove redundant queries and parameters

Now $self is actually an instance of the job class, there's no need to
have the job_id parameter passed, or the have the ->process method
re-fetch the object from the database.

This patch cleans things up.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>