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/armnn/BackendHelper.cpp b/src/armnn/BackendHelper.cpp
index 673950e..84889b8 100644
--- a/src/armnn/BackendHelper.cpp
+++ b/src/armnn/BackendHelper.cpp
@@ -6,7 +6,7 @@
 #include <armnn/BackendHelper.hpp>
 #include <armnn/BackendRegistry.hpp>
 
-#include <backendsCommon/IBackendInternal.hpp>
+#include <armnn/backends/IBackendInternal.hpp>
 
 namespace armnn
 {