manual/jobs.texi: remove unused var from example code

The do_job_notification() function defines a variable without using
it. Remove it.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

manual/job.texi

@@ -860,7 +860,6 @@ void
 do_job_notification (void)
 @{
   job *j, *jlast, *jnext;
-  process *p;
 
   /* @r{Update status information for child processes.}  */
   update_status ();