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/backendsCommon/WorkloadUtils.hpp b/src/backends/backendsCommon/WorkloadUtils.hpp
index 6fe8707..92ef2d2 100644
--- a/src/backends/backendsCommon/WorkloadUtils.hpp
+++ b/src/backends/backendsCommon/WorkloadUtils.hpp
@@ -6,7 +6,8 @@
 #pragma once
 
 #include "CpuTensorHandle.hpp"
-#include "ITensorHandle.hpp"
+
+#include <armnn/backends/ITensorHandle.hpp>
 
 #include <armnn/Tensor.hpp>