COMPMID-417: Remove val_to_string

The function was a duplicate of the to_string function we have in
support/ToolchainSupport.h

Change-Id: If1eff674333248f7d189824ced717310afec19b0
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/79634
Reviewed-by: Georgios Pinitas <georgios.pinitas@arm.com>
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
diff --git a/src/core/CL/kernels/CLPoolingLayerKernel.cpp b/src/core/CL/kernels/CLPoolingLayerKernel.cpp
index 08f0d4a..3777e3b 100644
--- a/src/core/CL/kernels/CLPoolingLayerKernel.cpp
+++ b/src/core/CL/kernels/CLPoolingLayerKernel.cpp
@@ -112,7 +112,7 @@
     build_opts.emplace(("-DPOOL_" + ((PoolingType::MAX == pool_type) ? std::string("MAX") : std::string("AVG"))));
 
     // Create kernel
-    std::string kernel_name = "pooling_layer_" + val_to_string(pool_size);
+    std::string kernel_name = "pooling_layer_" + support::cpp11::to_string(pool_size);
     _kernel                 = static_cast<cl::Kernel>(CLKernelLibrary::get().create_kernel(kernel_name, build_opts));
 
     // Set static kernel arguments