Valgrind: fix "definitely lost" memory in test - sqlite3test

==64824== 171 (88 direct, 83 indirect) bytes in 1 blocks are definitely lost in loss record 392 of 418
==64824==    at 0x4843FA3: operator new(unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==64824==    by 0x528A935: qof_session_new (qofsession.cpp:148)
==64824==    by 0x141832: main (sqlite3test.c:34)

bindings/python/sqlite3test.c

@@ -36,6 +36,7 @@ int main()
     qof_session_load(s, NULL);
     qof_session_save(s, NULL);
     qof_session_end(s);
+    qof_session_destroy(s);
     unlink(TESTFILE);
     return 0;
 }