Use DQMGenericClient instead of HLTTauPostProcessor

In favor of a common tool. DQMGenericClient does everything
HLTTauPostProcessor does except the EfficiencyRefPrevious plot.
HLTTauPostProcessor will be modified to produce only that in following
commits.
Remove trailing '/' from the DQMBaseFolder configuration
Rewrite HLTTauPostProcessor to produce only EfficiencyRefPrevious plot

Everything else is now done with DQMGenericClient.

Remove HLTTauDQMSummaryPlotter as obsolete.