IVGCVSW-4483 Remove boost::polymorphic_downcast

 * exchange boost::polymorphic_downcast with armnn::PolymorphicDowncast
 * remove unnecessary includes of boost::polymorphic_downcast

Signed-off-by: Jan Eilers <jan.eilers@arm.com>
Change-Id: Ie603fb82860fe05fee547dc78073230cc62b2e1f
diff --git a/src/backends/neon/workloads/NeonRsqrtWorkload.cpp b/src/backends/neon/workloads/NeonRsqrtWorkload.cpp
index b629283..44980df 100644
--- a/src/backends/neon/workloads/NeonRsqrtWorkload.cpp
+++ b/src/backends/neon/workloads/NeonRsqrtWorkload.cpp
@@ -9,8 +9,8 @@
 
 #include <aclCommon/ArmComputeTensorHandle.hpp>
 #include <aclCommon/ArmComputeTensorUtils.hpp>
+#include <armnn/utility/PolymorphicDowncast.hpp>
 
-#include <boost/cast.hpp>
 
 namespace armnn
 {
@@ -28,8 +28,8 @@
 {
     m_Data.ValidateInputsOutputs("NeonRsqrtWorkload", 1, 1);
 
-    arm_compute::ITensor& input  = boost::polymorphic_downcast<IAclTensorHandle*>(m_Data.m_Inputs[0])->GetTensor();
-    arm_compute::ITensor& output = boost::polymorphic_downcast<IAclTensorHandle*>(m_Data.m_Outputs[0])->GetTensor();
+    arm_compute::ITensor& input  = PolymorphicDowncast<IAclTensorHandle*>(m_Data.m_Inputs[0])->GetTensor();
+    arm_compute::ITensor& output = PolymorphicDowncast<IAclTensorHandle*>(m_Data.m_Outputs[0])->GetTensor();
 
     m_RsqrtLayer.configure(&input, &output);
 }