IVGCVSW-4246 Clean build of LayerTests with -Wextra

Change-Id: If3d98e45a6e2fa8e1afd19a4052334335feacf63
Signed-off-by: Derek Lamberti <derek.lamberti@arm.com>
diff --git a/src/backends/backendsCommon/test/layerTests/SliceTestImpl.cpp b/src/backends/backendsCommon/test/layerTests/SliceTestImpl.cpp
index a60b189..65b1716 100644
--- a/src/backends/backendsCommon/test/layerTests/SliceTestImpl.cpp
+++ b/src/backends/backendsCommon/test/layerTests/SliceTestImpl.cpp
@@ -30,6 +30,7 @@
     const float qScale = 1.0f,
     const int qOffset = 0)
 {
+    boost::ignore_unused(memoryManager);
     if(armnn::IsQuantizedType<T>())
     {
         inputInfo.SetQuantizationScale(qScale);