The `doMergedHLTResult` was used to distinguish Run-1 where we had a
split-level HLT (L2+EF) from Run-2 and beyond. But the same information
is available via the `EDMVersion` flag.

Also cleanup configuration of Run-2 DataScouting unpacking and always
set L2/EF/HLTResultKeys explicitly instead of relying on defaults.