Fix memory leak in HWUI

std::unique_ptr::release just releases the ownership of the
managed object. To delete the object, std::unique_ptr::reset
function should be called.

Change-Id: If65f74085b1fc2be3a9fffc433326e0bcdb40ff3
diff --git a/libs/hwui/Layer.cpp b/libs/hwui/Layer.cpp
index e16865e..62eeb43 100644
--- a/libs/hwui/Layer.cpp
+++ b/libs/hwui/Layer.cpp
@@ -251,7 +251,7 @@
 void Layer::cancelDefer() {
     renderNode = nullptr;
     deferredUpdateScheduled = false;
-    deferredList.release();
+    deferredList.reset(nullptr);
 }
 
 void Layer::flush() {