clean up unused code and options

[DeniseWorthen]

• The module_MEDIATOR, module_MEDIATOR_methods and the module_MEDIATOR_SpaceWeather should be removed.

• Various legacy ifdef settings (eg. ifdef CMEPS, if ESMF_VERSION_MAJOR < 8) as well as non-existent or legacy models (ifdef FRONT_GSM) should be removed.

• The large block of code for adding entries to the Field Dictionary should be removed and the fd_nems.yaml used instead.

• The bail-out error checking lines should be simplified by adding a similar ChkErr function present in the MOM6 NUOPC cap and CMEPS.