refactor: adapt to the change of NATIVE -> NAT on backend

To keep things consistent, we changed the TotalFunction enum value
for native totals from NATIVE to NAT on the backend. This is the
adaptation to that.

JIRA: CQ-652
risk: low

Author: no23reason

gooddata-sdk/gooddata_sdk/compute/model/execution.py

@@ -175,20 +175,13 @@ def _create_totals(self) -> Optional[list[models.Total]]:
                 models.Total(
                     local_identifier=total.local_id,
                     metric=total.metric_local_id,
-                    function=ExecutionDefinition._convert_total_aggregation(total.aggregation),
+                    function=total.aggregation.upper(),
                     total_dimensions=total_dims,
                 )
             )
 
         return totals
 
-    @staticmethod
-    def _convert_total_aggregation(aggregation: str) -> str:
-        # native total is represented as NAT in visualization objects, but needs to be NATIVE in execution
-        if aggregation.upper() == "NAT":
-            return "NATIVE"
-        return aggregation.upper()
-
     def _create_result_spec(self) -> models.ResultSpec:
         dimensions = self._create_dimensions()
         totals = self._create_totals()