Revert "Fix potential fd leak in listener_read_cb()"

Revert "Fix potential fd leak in listener_read_cb()"

This reverts commit a695a720cda892c270736d127333d73553842094.

@kgraefe:
  "I believe that this commit is just wrong: if lev->cnt is not 1 after
  the callback, new_fd will still never be closed in listener_read_cb().
  So in that case it is the responsibility of the user's code to close
  the file descriptor (which is fine). But why shouldn't it be in the
  other case? And how does the user's code know?"

And I agree