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/test/BackendRegistryTests.cpp b/src/backends/backendsCommon/test/BackendRegistryTests.cpp
index e1ab7ec..172c0a9 100644
--- a/src/backends/backendsCommon/test/BackendRegistryTests.cpp
+++ b/src/backends/backendsCommon/test/BackendRegistryTests.cpp
@@ -6,7 +6,7 @@
 #include <armnn/Types.hpp>
 #include <armnn/BackendRegistry.hpp>
 
-#include <backendsCommon/IBackendInternal.hpp>
+#include <armnn/backends/IBackendInternal.hpp>
 
 #include <boost/test/unit_test.hpp>