CLN: Remove unused context manager in groupby code

@@ -2875,19 +2875,13 @@ def sum_compat(obj: NDFrameT):                 # GH#18588: see min_compat below                 return obj.sum(skipna=skipna) -            # If we are grouping on categoricals we want unobserved categories to-            # return zero, rather than the default of NaN which the reindexing in-            # _agg_general() returns. GH #31422-            with com.temp_setattr(self, "observed", True):-                result = self._agg_general(-                    numeric_only=numeric_only,-                    min_count=min_count,-                    alias="sum",-                    npfunc=sum_compat,-                    skipna=skipna,-                )--            return result+            return self._agg_general(+                numeric_only=numeric_only,+                min_count=min_count,+                alias="sum",+                npfunc=sum_compat,+                skipna=skipna,+            )      @final     def prod(