B2OC: fix to make_dsst_to_dsplusgamma in builders/d_builder.py

fix to make_dsst_to_dsplusgamma in builders/d_builder.py and related changes in b_to_dh.py and b_to_dhh.py

this fix is related to the update of the code proposed here:

https://gitlab.cern.ch/lhcb/Moore/-/tree/sstahl_b2ocfix

but for self consistency a sligly different solution was implemented and tested (4 stripping lines are affected overall)