You can select the nested sequence, then hold shift and drag the playhead to each marker individually, press M, and hit “delete”. Might have to do it twice to get it to disappear on both the video and audio tracks. However to delete them all at once, I have no idea. I have a sequence with a lot of markers and I’m trying to delete them all, and can’t seem to find a way. Since you seem to only have a few though hopefully that will help.