[MINOR] Silence compiler warnings (unnecessary switch default)

Replacing switch default cases where all cases are covered with an exception as this should never happen.

src/runtime/local/kernels/EwUnarySca.h

@@ -95,9 +95,7 @@ EwUnaryScaFuncPtr<VTRes, VTArg> getEwUnaryScaFuncPtr(UnaryOpCode opCode) {
         // Comparison.
         MAKE_CASE(UnaryOpCode::ISNAN)
 #undef MAKE_CASE
-    default:
-        throw std::runtime_error("unknown UnaryOpCode: " +
-                                 std::to_string(static_cast<int>(opCode)));
+        throw std::runtime_error("unknown UnaryOpCode: " + std::to_string(static_cast<int>(opCode)));
     }
     if (!res)
         throw std::runtime_error(

src/runtime/local/kernels/Group.h

@@ -70,24 +70,19 @@ VTRes aggregate(const mlir::daphne::GroupEnum &aggFunc, const VTArg *begin,
     using mlir::daphne::GroupEnum;
     switch (aggFunc) {
     case GroupEnum::COUNT:
-        return end - begin;
-        break; // TODO: Do we need to check for Null elements here?
+        return end - begin;// TODO: Do we need to check for Null elements here?
     case GroupEnum::SUM:
         return std::accumulate(begin, end, (VTRes)0);
-        break;
     case GroupEnum::MIN:
         return *std::min_element(begin, end);
-        break;
     case GroupEnum::MAX:
         return *std::max_element(begin, end);
-        break;
     case GroupEnum::AVG:
         return std::accumulate(begin, end, (double)0) / (double)(end - begin);
-        break;
-    default:
-        return *begin;
-        break;
+//    default:
+//        return *begin;
     }
+    throw std::runtime_error("unknown value of mlir::daphne::GroupEnum");
 }
 
 // struct which calls the aggregate() function (specified via aggFunc) on each