Remove override of threads for C386 fcst

There was a line that was overriding the previous selection for the
number of threads when running at C384.

Also changed the settings to use the correct number of threads when
running the free forecast vs gdas.

Refs: NOAA-EMC#416

parm/config/config.resources

@@ -206,7 +206,6 @@ elif [ $step = "fcst" ]; then
 
         export nth_fcst=${nth_fv3:-2}
 
-        if [[ "$CASE" == "C384" ]]; then nth_fcst=4; fi
         export npe_node_fcst=$(echo "$npe_node_max / $nth_fcst" | bc)
         if [[ "$machine" == "WCOSS_C" ]]; then export memory_fcst="1024M"; fi