STYLE: prefer listReduce() to using listCombineReduce() when possible

- potentially allows access into the builtin MPI operations

applications/utilities/postProcessing/miscellaneous/postChannel/channelIndexTemplates.C

@@ -40,7 +40,7 @@ Foam::Field<T> Foam::channelIndex::regionSum(const Field<T>& cellField) const
     }
 
     // Global sum
-    Pstream::listCombineReduce(regionField, plusEqOp<T>());
+    Pstream::listReduce(regionField, sumOp<T>());
 
     return regionField;
 }