fix up refcount/properties test case

fix up refcount/properties test case

Recent changes to the properties testcase made invalid use of the GArray
free function.  This free function takes a pointer to the item to be
freed, not the item itself.  Since that item was a pointer to a GObject,
g_object_unref() was getting a GObject**, rather than a GObject*.

The use of GArray in this testcase is pretty questionable in the first
place, so just use C arrays instead.