Revert "Fix decimal agg signature on partial companion function (#465)"

This reverts commit 336d61f.

Author: zhztheplayer

velox/functions/sparksql/aggregates/AverageAggregate.cpp

@@ -444,10 +444,9 @@ exec::AggregateRegistrationResult registerAverage(
               if (inputType->isShortDecimal()) {
                 auto inputPrecision = inputType->asShortDecimal().precision();
                 auto inputScale = inputType->asShortDecimal().scale();
-                auto sumType = getDecimalSumType(inputPrecision, inputScale);
-                if (exec::isPartialOutput(step) ||
-                    (step == core::AggregationNode::Step::kSingle &&
-                     resultType->isRow())) {
+                auto sumType =
+                    DECIMAL(std::min(38, inputPrecision + 10), inputScale);
+                if (exec::isPartialOutput(step)) {
                   return std::make_unique<
                       DecimalAverageAggregate<int64_t, int64_t>>(
                       resultType, sumType);

velox/functions/sparksql/aggregates/SumAggregate.cpp

@@ -29,13 +29,7 @@ using SumAggregate = SumAggregateBase<TInput, TAccumulator, ResultType, true>;
 TypePtr getDecimalSumType(
     const TypePtr& resultType,
     core::AggregationNode::Step step) {
-  if (exec::isPartialOutput(step)) {
-    return resultType->childAt(0);
-  }
-  if (step == core::AggregationNode::Step::kSingle && resultType->isRow()) {
-    return resultType->childAt(0);
-  }
-  return resultType;
+  return exec::isPartialOutput(step) ? resultType->childAt(0) : resultType;
 }
 } // namespace