IVGCVSW-4210 Create a public API for the common backend files

 * Create a public API for the common backend files
 * Move OutputHandler to armnn internal
 * Remove unused headers

Signed-off-by: Matteo Martincigh <matteo.martincigh@arm.com>
Signed-off-by: Narumol Prangnawarat <narumol.prangnawarat@arm.com>
Change-Id: I3e86d908b021e3561befa9d45158d87d2cbb18c0
diff --git a/src/backends/reference/workloads/RefMeanWorkload.hpp b/src/backends/reference/workloads/RefMeanWorkload.hpp
index eb4b407..c673f94 100644
--- a/src/backends/reference/workloads/RefMeanWorkload.hpp
+++ b/src/backends/reference/workloads/RefMeanWorkload.hpp
@@ -5,8 +5,8 @@
 
 #pragma once
 
-#include "backendsCommon/Workload.hpp"
-#include "backendsCommon/WorkloadData.hpp"
+#include <backendsCommon/Workload.hpp>
+#include <backendsCommon/WorkloadData.hpp>
 
 #include "Decoders.hpp"
 #include "Encoders.hpp"