[ONNX] Remove unnecesary Mean in opset 8 (#4053)

* [ONNX] Remove unnecesary Mean in opset 8

* Use opset1 instead of v1

* Fix merge artifact

* Use opset1 Divide instead of opset0
Co-authored-by: Robert Kimball <robert.kimball@intel.com>

src/ngraph/frontend/onnx_import/op/mean.cpp

@@ -16,10 +16,6 @@
 
 #include "mean.hpp"
 #include "default_opset.hpp"
-#include "ngraph/op/add.hpp"
-#include "ngraph/op/constant.hpp"
-#include "ngraph/op/divide.hpp"
-#include "ngraph/opsets/opset0.hpp"
 #include "utils/variadic.hpp"
 
 namespace ngraph
@@ -29,25 +25,6 @@ namespace ngraph
         namespace op
         {
             namespace set_1
-            {
-                NodeVector mean(const Node& node)
-                {
-                    auto sum = variadic::make_ng_variadic_op<ngraph::opset0::Add>(node).front();
-                    auto shape = sum->get_shape();
-
-                    // Create a Constant representing the number of inputs with the same shape as
-                    // sum
-                    auto count = default_opset::Constant::create(
-                        sum->get_element_type(),
-                        shape,
-                        std::vector<int>(shape_size(shape), node.get_ng_inputs().size()));
-
-                    return {sum / count};
-                }
-
-            } // namespace set_1
-
-            namespace set_8
             {
                 NodeVector mean(const Node& node)
                 {
@@ -61,10 +38,10 @@ namespace ngraph
                         shape,
                         std::vector<int>(shape_size(shape), node.get_ng_inputs().size()));
 
-                    return {sum / count};
+                    return {std::make_shared<default_opset::Divide>(sum, count)};
                 }
 
-            } // namespace set_8
+            } // namespace set_1
 
         } // namespace op
 

src/ngraph/frontend/onnx_import/op/mean.hpp

@@ -31,12 +31,6 @@ namespace ngraph
 
             } // namespace set_1
 
-            namespace set_8
-            {
-                NodeVector mean(const Node& node);
-
-            } // namespace set_1
-
         } // namespace op
 
     } // namespace onnx_import

src/ngraph/frontend/onnx_import/ops_bridge.cpp

@@ -301,7 +301,6 @@ namespace ngraph
             REGISTER_OPERATOR("Max", 1, max);
             REGISTER_OPERATOR("Max", 8, max);
             REGISTER_OPERATOR("Mean", 1, mean);
-            REGISTER_OPERATOR("Mean", 8, mean);
             REGISTER_OPERATOR("MeanVarianceNormalization", 1, mean_variance_normalization);
             REGISTER_OPERATOR("MeanVarianceNormalization", 9, mean_variance_normalization);
             REGISTER_OPERATOR("Min", 1, min);