IVGCVSW-5300 Remove some boost::numeric_cast from armnn/backends

 * Replaced with armnn/utility/NumericCast.hpp
 * Some exclusions in reference backend
 * Excluded as requires float implementation in NumericCast.hpp

Signed-off-by: Matthew Sloyan <matthew.sloyan@arm.com>
Change-Id: I9e4e9cd502c865452128fa04415fd6f250baa855
diff --git a/src/backends/reference/RefLayerSupport.cpp b/src/backends/reference/RefLayerSupport.cpp
index 5e3c96d..52c079f 100644
--- a/src/backends/reference/RefLayerSupport.cpp
+++ b/src/backends/reference/RefLayerSupport.cpp
@@ -9,17 +9,14 @@
 #include <armnn/Types.hpp>
 #include <armnn/Descriptors.hpp>
 #include <armnn/utility/IgnoreUnused.hpp>
+#include <armnn/utility/NumericCast.hpp>
 
 #include <LayerSupportCommon.hpp>
 #include <backendsCommon/LayerSupportRules.hpp>
 
-#include <boost/cast.hpp>
-
 #include <vector>
 #include <array>
 
-using namespace boost;
-
 namespace armnn
 {
 
@@ -1326,7 +1323,7 @@
     }
     else
     {
-        auto outputDim = input.GetNumDimensions() - boost::numeric_cast<unsigned int>(descriptor.m_Axis.size());
+        auto outputDim = input.GetNumDimensions() - armnn::numeric_cast<unsigned int>(descriptor.m_Axis.size());
 
         if (outputDim > 0)
         {