Prune commentary and stale Rust port notes

core/src/primitive/layer.rs

@@ -14,19 +14,13 @@ struct LayerNode<T> {
 
 #[derive(Clone, Copy, Debug)]
 enum Ptr {
-    /// continue on same level
     Next(usize),
-    /// go back to parent
     Parent(usize),
-    /// end
     None,
 }
 
-/// TODO: currently this does not ever free layers
-/// is that realistically desired?
 pub struct Layers<T> {
     vec: Vec<LayerNode<T>>,
-    /// index of last layer at top level (start at first = 0)
     last: usize,
 }
 
@@ -36,9 +30,6 @@ struct Child {
     tail: usize,
 }
 
-/// The draw order of every layer. The primitives themselves live in one
-/// arena beside this (`UiRenderState::primitives`); a layer names the
-/// slots it draws, which is what its vertex buffer is.
 pub type PrimitiveLayers = Layers<LayerOrder>;
 
 impl<T: Default> Layers<T> {