Delete unused "use" statements and variables

Also cleaned up a comment when I realized I wrote the comment and wasn't sure
what it meant

Author: mnlevy1981

config_src/drivers/nuopc_cap/mom_cap.F90

@@ -588,8 +588,8 @@ subroutine InitializeAdvertise(gcomp, importState, exportState, clock, rc)
   Ice_ocean_boundary%ice_ncat = 0
   if (cesm_coupled) then
     ! Note that flds_i2o_per_cat is set by the env_run.xml variable CPL_I2O_PER_CAT
-    ! This xml variable is set by MOM_interface's buildnml script; it has the same
-    ! value as USE_MARBL in the case
+    ! In CESM, this xml variable is set by MOM_interface's buildnml script and by
+    ! default it is false unless ICE_NCAT>0 and USE_MARBL_TRACERS=True
     call NUOPC_CompAttributeGet(gcomp, name='flds_i2o_per_cat', value=cvalue, rc=rc)
     if (ChkErr(rc,__LINE__,u_FILE_u)) return
     read(cvalue,*) i2o_per_cat

config_src/drivers/nuopc_cap/mom_cap_methods.F90

@@ -89,7 +89,6 @@ subroutine mom_import(ocean_public, ocean_grid, importState, ice_ocean_boundary,
   real(ESMF_KIND_R8), allocatable :: tauy(:,:)
   real(ESMF_KIND_R8), allocatable :: stkx(:,:,:)
   real(ESMF_KIND_R8), allocatable :: stky(:,:,:)
-  logical                         :: med_has_co2
   character(len=*)  , parameter   :: subname = '(mom_import)'
 
   rc = ESMF_SUCCESS

src/tracer/MARBL_tracers.F90

@@ -41,7 +41,6 @@ module MARBL_tracers
 use MARBL_interface,              only : MARBL_interface_class
 use MARBL_interface_public_types, only : marbl_diagnostics_type, marbl_saved_state_type
 
-use coupler_types_mod,      only : coupler_type_set_data, ind_csurf
 use atmos_ocean_fluxes_mod, only : aof_set_coupler_flux
 
 implicit none ; private