IVGCVSW-4873 Implement Pimpl Idiom for INetwork and IOptimizedNetwork

!android-nn-driver:5042

Signed-off-by: Kevin May <kevin.may@arm.com>
Change-Id: Ia1ce8b839e81b46428ba0f78463e085e5906958d
Signed-off-by: Francis Murtagh <francis.murtagh@arm.com>
Signed-off-by: Finn Williams <Finn.Williams@arm.com>
diff --git a/src/armnn/Runtime.cpp b/src/armnn/Runtime.cpp
index 8fdc4f1..9cc7b2c 100644
--- a/src/armnn/Runtime.cpp
+++ b/src/armnn/Runtime.cpp
@@ -135,7 +135,7 @@
     }
 
     unique_ptr<LoadedNetwork> loadedNetwork = LoadedNetwork::MakeLoadedNetwork(
-        std::unique_ptr<OptimizedNetwork>(PolymorphicDowncast<OptimizedNetwork*>(rawNetwork)),
+        std::unique_ptr<IOptimizedNetwork>(rawNetwork),
         errorMessage,
         networkProperties,
         m_ProfilingService);