The liners are there to improve or assist the structural integrity of the joint between the sides, top and bottom. They are sometimes (typically) kerf cut to facilitate conforming to the bend of the sides. Linings are almost mandatory if there is going to be a binding because of the thin-ness of the sides.
With no bindings, liners can be eliminated but not typically. The trade off would be the thickness of the sides.
Edit; Chuck, assuming we started at the same time, you must type 3 minutes faster than I do. :~)