RichSmartID : Retire HPD support, add XPD for U2 studies

HPD support is retained as part of the legacy RichSmartID32 channel identifier class, which RichDet has previously been updated to use (to retain Run2 support where needed via DetDesc). New XPDs for Upgrade 2 will only be supported in dd4hep going forward. MaPMTs for run3 are supported by both RichSmartID and RichSmartID32. Note XPD refers to the fact we have not decided yet what the PDs will be in U2, so this type is used in the meantime.