TrigConfigSvc: remove usage of IJobOptionsSvc

Remove usage of the deprecated IJobOptionSvc from legacy trigger configuration code:

DSConfigSvc:

• Query the list of folders directly via IIOVDbSvc instead of reading its property from the JobOptionsSvc.

HLTConfigSvc:

• In order to avoid migrating to IOptionsSvc, remove all code related to reading prescales in a partition for the legacy trigger as we don't support this anymore.

None of this should have an impact on the Run-3 trigger. There will be a separate MR for the TrigConf::JobOptionsSvc, which will need more thorough testing.

cc @stelzer @mark @rbielski