Removing old sensitive detector package for HGTD
Removing currently completely unused old HGTDG4SD package under LAr, in favor of new code which will go into HGTD_ReadoutGeometry, towards https://its.cern.ch/jira/browse/ATLSWUPGR-92. As discussed with @jchapman earlier.
Tagging @dshope and @aleopold for info.
Best, Christian