core: transition job to JOB_FINISHED on uninstall

core: transition job to JOB_FINISHED on uninstall

When a job reaches the job_uninstall() stage we used to set the
state to JOB_WAITING. However now that we have a JOB_FINISHED state [1]
we should use that instead. This is more accurate so when
varlink_job_send_removed_signal() is called the job is in the expected
state and that is what the user will see.

Note that this does not change the D-Bus API because there
bus_job_send_removed_signal() doesn't send the state, it only sends
the result.

[1] https://github.com/systemd/systemd/pull/41811