Overhaul carbon_gases_mod.F90 to obtain fields and apply chemistry ba…

…sed on species defined

In carbon_gases_mod.F90 all chemistry input fields needed for CO2, CH4, and CO
chemistry were obtained regardless of the species included in the carbon simulation.
Therefore when running the carbon simulation with only one species (e.g. CO2)
fields were being obtained that weren't necessary. These fields have been
blocked by logical statements checking if the species that needs those fields is
advected.

Also in this module, the chemistry routine has been updated to only call
KPP when CH4 and/or CO are defined as advected species. KPP is not needed
for CO2-only simulations. Instead CO2-only simulations utilize the CO2_COPROD
field obtained from HEMCO. This field was originally obtained and applied
to the species concentration array in subroutine Emiss_Carbon_Gases. The
routine name was misleading and has been renamed to CO2_Production. The call
to this routine has also been moved from emissions_mod.F90 to Chem_Carbon_Gases
in carbon_gases_mod.F90.

Notes: When we retire the CO2 simulation, we should be able to also remove
the CO2 menu from geoschem_config.yml since it is not needed when using
CO2 in the carbon simulation.

Signed-off-by: Melissa Sulprizio <[email protected]>