epol: Sanitize epoll tfds collecting

This case is legacy, tfds are merged into epoll entry, but
to make it working we have separate list of tfds and extra
code in ->open callback.

Keep the legacy code in one place.

Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>