The forest is mapped twice:
- as a simple polygon https://www.openstreetmap.org/way/866019680
- as a large relation https://www.openstreetmap.org/relation/54847
So the large polygons can be deleted I think?
Note that IMHO it doesn't really make sense to have that many inners on the Foret dominial  de Mormal: it's not because the current landcover happens to be clearcut, that it's not part of the forest anymore.