I have about 100 clips in which I have set in and out points for. But now, I just want to put all the clips into a sequence, in their full lenghts. Is there a way to select them all or clear the clip markers to all of them, instead of opening each one and manually clearing the markers for each one?

Not to my knowledge unfortunately.

Why not just grab all the original clips from the browser and drop them into a new timeline?