Remove raw_line_seg_label, paragraphs_label, pages_label

Only one label is used, raw_line_seg_label, paragraphs_label, pages_label should be removed. All occurrences of raw_line_seg_label, paragraphs_label, pages_label must be removed, see https://gitlab.com/teklia/atr/dan/-/blob/66f0f92db68d23c1312c617c8556169b5423e18c/dan/manager/dataset.py#L278.