Remove header and footer support,this is unnecessary

doric-demo/src/FlowLayoutDemo.ts

@@ -21,14 +21,6 @@ class FlowDemo extends Panel {
             columnCount: 3,
             columnSpace: 10,
             rowSpace: 10,
-            header: flowItem(image({
-                layoutConfig: layoutConfig().mostWidth().fitHeight(),
-                imageUrl: imageUrls[0]
-            })),
-            footer: flowItem(image({
-                layoutConfig: layoutConfig().mostWidth().fitHeight(),
-                imageUrl: imageUrls[1]
-            })),
             renderItem: (idx) => {
                 return flowItem(
                     text({

doric-demo/src/ListDemo.ts

@@ -47,12 +47,6 @@ class ListVH extends ViewHolder {
                     height: 50,
                 }),
                 this.list = list({
-                    header: listItem(text({
-                        text: "This is header",
-                    })),
-                    footer: listItem(text({
-                        text: "This is footer",
-                    })),
                     itemCount: 0,
                     layoutConfig: {
                         widthSpec: LayoutSpec.MOST,