Restored test that was commented out when working on LSTM

Change-Id: I161a832e4e53cf014a3d57784bd2f0bffbd633b5
diff --git a/src/backends/test/IsLayerSupportedTestImpl.hpp b/src/backends/test/IsLayerSupportedTestImpl.hpp
index 867f7f2..1bcf56d 100644
--- a/src/backends/test/IsLayerSupportedTestImpl.hpp
+++ b/src/backends/test/IsLayerSupportedTestImpl.hpp
@@ -418,8 +418,7 @@
         try
         {
             bool retVal = LayerPolicy::MakeDummyWorkload(factory, numIn, numOut).get() != nullptr;
-            // hacky way (it has to be replaced): for Lstm, we only support F32 right now
-//            BOOST_CHECK_MESSAGE(retVal, layerName << errorMsg);
+            BOOST_CHECK_MESSAGE(retVal, layerName << errorMsg);
             return retVal;
         }
         catch(const armnn::InvalidArgumentException& e)