PyCintex cleanup in PhysicsAnalysis (from master)

Migration to cppyy, removal in some places where it is apparently not
needed.  Some packages modified might have been broken anyhow since the
ROOT6 migration - if they happen to be still in use, they will need
extra work to fix.
This is cherry-picked d1f78e60 [formerly ed45654d] from
master to solve ATEAM-436


Former-commit-id: 3e1eb566