Remove 'advCells' from init_atmosphere input and output streams

The 'advCells' field is only used internally by the atm_initialize_advection_rk
subroutine, and it is therefore not necessary to write this field to the output
stream nor to read it from the input stream in the init_atmosphere core.

src/core_init_atmosphere/Registry.xml

@@ -410,7 +410,6 @@
                         <var name="ol3" packages="vertical_stage_in;met_stage_in"/>
                         <var name="ol4" packages="vertical_stage_in;met_stage_in"/>
                         <var name="deriv_two" packages="gwd_stage_in;vertical_stage_in;met_stage_in"/>
-                        <var name="advCells" packages="gwd_stage_in;vertical_stage_in;met_stage_in"/>
                         <var name="defc_a" packages="gwd_stage_in;vertical_stage_in;met_stage_in"/>
                         <var name="defc_b" packages="gwd_stage_in;vertical_stage_in;met_stage_in"/>
                         <var name="coeffs_reconstruct" packages="gwd_stage_in;vertical_stage_in;met_stage_in"/>
@@ -507,7 +506,6 @@
                         <var name="ol3" packages="gwd_stage_out;vertical_stage_out;met_stage_out"/>
                         <var name="ol4" packages="gwd_stage_out;vertical_stage_out;met_stage_out"/>
                         <var name="deriv_two"/>
-                        <var name="advCells"/>
                         <var name="defc_a"/>
                         <var name="defc_b"/>
                         <var name="coeffs_reconstruct"/>