Fix dns/leak_resume_send_err test.

Fix dns/leak_resume_send_err test.

Because we don't cancel request,
and want our callback to recieve DNS_ERR_SHUTDOWN,
we use deferred callback, and there was
- one extra malloc(),
  @see reply_schedule_callback()
- and one missing free
  @see request_finished() (req->handle->pending_cb = 1)
than we don't need to count in testleak_cleanup()

So just decrement allocated_chunks to 2,
like we already take care about it.