pool: Clean up job scheduler used for HSM

Addresses code smell in SimpleJobScheduler. The output format of
'rh jobs ls' and 'st jobs ls' is changed as the priority, client
and client ID are no longer shown - these fields were not used
and always contained the same value for HSM jobs.

JobScheduler and its implementation is only used by HSM jobs
and thus much of its functionality was unused. The patch
removes a lot of dead code.

Target: trunk
Require-notes: yes
Require-book: yes
Acked-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Patch: http://rb.dcache.org/r/5480/