IVGCVSW-2060: Separate and move backend specific unit tests from the src/armnn/test folder to the backends

* Moved backend-specific memory leak checking tests from RuntimeTests.cpp to
  the corresponding backend test folder

Change-Id: I0a7f4ef52c5350c3cebca23b2b4e61a9446ca11f
diff --git a/src/backends/reference/backend.mk b/src/backends/reference/backend.mk
index 9ecb6d7..455ab46 100644
--- a/src/backends/reference/backend.mk
+++ b/src/backends/reference/backend.mk
@@ -66,4 +66,5 @@
 BACKEND_TEST_SOURCES := \
         test/RefCreateWorkloadTests.cpp \
         test/RefLayerSupportTests.cpp \
-        test/RefLayerTests.cpp
+        test/RefLayerTests.cpp \
+        test/RefRuntimeTests.cpp