Replace remaining std::auto_ptr<> with wxScopedPtr in the tests

This should have been done in b8c9cd3528
to avoid all warnings about std::auto_ptr<> being deprecated when using
g++ 6 or later which compiles in C++14 mode by default.

tests/archive/archivetest.cpp

@@ -20,7 +20,6 @@
 
 #include "archivetest.h"
 #include "wx/dir.h"
-#include "wx/scopedptr.h"
 #include <string>
 #include <list>
 #include <map>