Removing Wt_*_onshellW modules - AGENE-1819
requested to merge atlas-physics/pmg/mcexperts/powheg-experts/athena:21.6-RemoveWt_onshell_modules into 21.6
Removing the Wt_DR_onshellW.py and Wt_DS_onshellW.py modules, as discussed in !33708 (merged).