dict: Unref dict connection immediately when connection is destroyed

dict: Unref dict connection immediately when connection is destroyed

The delayed unrefing is needed when calling from dict command callbacks to
avoid calling dict_deinit() too early. But the connection's destroy() vfunc
can't be called directly from dict command callbacks, so there's no need
to add further delays. Especially when this happens at deinit where there is
no possibility of calling the delayed callback anymore.