Contours > Remove is a set of functions that remove things from the active Patch object, usually so you can start over.
Contours > Remove > Curvature Lines removes the black place-holders and orange curvature lines that that are the result of Contours > Detect Curvature.
Contours > Remove > Subdivision/Extension (applicable after Contours > Subdivide / Extend Contours, or after Patches > Construct Patches if extension was performed) - removes the contour patches that exist around yellow contour lines and the customized subdivisions that may have been performed on yellow or orange contour lines.
Contours > Remove > Contour Lines removes the yellow (extendable) and orange (unextendable) contour lines that that are the result of Contours > Detect Contours.