Some fixes to pythia8 interface suggested many years ago

Some fixes to pythia8 interface suggested many years ago, see AGENE-1926

the following corrections are to be added to Py8_i:

Pythia8_i l. 182 remove commented out line
// Does not exist

Pythia8B_i l.195 should be warning not info
/// Cannot find.

Pythia8_i header - rm. JAmes Monk's name
/// Why?

                rm commented out line 83
/// Done

CheckForFinalPartons.cxx l. 7-11 can probably be removed
/// Guessing about comments in lines 13-23

CheckForFinalPartons.h l. 17

I suspect this one and the one below are virtual methods? If yes, please mark them virtual and override.
/// Done. One method is override.

HllgamRepeatTimeShower.h

l. 14-27

Please mark all re-implemented methods as virtual and override.
/// Done

UserPhotonFlux.cxx l.17
Is blank initialize needed? Also INFO logging level is maybe a bit too verbose.
///It is not empty anymore.

UserPhotonFlux.cxx l.48

Is empty finalize needed?
///It is not empty anymore.

UserPhotonFlux.h l. 75-90

Same comment here for virtual methods.
/// Done.

Pythia8_i.cxx l.581

I suspect there's motivation for std::cout here as it was present before, but please confirm.
/// There are some couts. Let it be so.

DecayToSUEP.cxx l.8

Can you please remove the commented-out lines?
/// There are no meaningful lines to remove.

GravFlat.cxx

put back Copyright
/// It seems the copyright is there

rm l. 27 
/// The line is commented out

Tag @ewelina