Higgs: delete unused DPD packages

Delete the following obsolete DPD-related Higgs packages and a few other files relying on them:

• HiggsD3PDMaker
• HSG2Event
• HSG5DPDUtils (was already disabled in build)
• HSG1DPDUtils
• HSG1AnalysisCommon (only one script)

cc @kkoeneke in the unlikely case any of this is still relevant.