Do not use deprecated ReleaseCleared in protobuf library.

This is to make code work with protobuf arenas for memory
management (ReleaseCleared is incompatible).
The cleaning of the memory is also simpler.

modules/dnn/src/caffe/caffe_importer.cpp

@@ -306,16 +306,13 @@ public:
 
         caffe::LayerParameter* binLayer = netBinary.mutable_layer(li);
         const int numBlobs = binLayer->blobs_size();
+        std::vector<caffe::BlobProto*> blobs(numBlobs);
+        binLayer->mutable_blobs()->ExtractSubrange(0, numBlobs, blobs.data());
         layerParams.blobs.resize(numBlobs);
         for (int bi = 0; bi < numBlobs; bi++)
         {
-            blobFromProto(binLayer->blobs(bi), layerParams.blobs[bi]);
-        }
-        binLayer->clear_blobs();
-        CV_Assert(numBlobs == binLayer->blobs().ClearedCount());
-        for (int bi = 0; bi < numBlobs; bi++)
-        {
-            delete binLayer->mutable_blobs()->ReleaseCleared();
+            blobFromProto(*blobs[bi], layerParams.blobs[bi]);
+            delete blobs[bi];
         }
     }