IVGCVSW-5299 Remove some boost::numeric_cast from armnn/tests

 * Replaced with armnn/utility/NumericCast.hpp
 * Removed combinations without float implementation in NumericCast.hpp

Signed-off-by: Matthew Sloyan <matthew.sloyan@arm.com>
Change-Id: Ia4ec605f063cdb0071fff302ef48c610f9f9505e
diff --git a/tests/MnistDatabase.cpp b/tests/MnistDatabase.cpp
index 9abc3a6..bbeb8ca 100644
--- a/tests/MnistDatabase.cpp
+++ b/tests/MnistDatabase.cpp
@@ -6,8 +6,6 @@
 
 #include <armnn/Logging.hpp>
 
-#include <boost/numeric/conversion/cast.hpp>
-
 #include <fstream>
 #include <vector>
 
@@ -94,7 +92,8 @@
 
     for (unsigned int i = 0; i < col * row; ++i)
     {
-        inputImageData[i] = boost::numeric_cast<float>(I[i]);
+        // Static_cast of unsigned char is safe with float
+        inputImageData[i] = static_cast<float>(I[i]);
 
         if(m_ScaleValues)
         {