[improvement] Sidebar: use relation mixin

packages/sidebar/index.js

@@ -1,8 +1,11 @@
 import { use } from '../utils';
+import { ParentMixin } from '../mixins/relation';
 
 const [sfc, bem] = use('sidebar');
 
 export default sfc({
+  mixins: [ParentMixin('vanSidebar')],
+
   props: {
     activeKey: {
       type: [Number, String],
@@ -10,18 +13,6 @@ export default sfc({
     }
   },
 
-  provide() {
-    return {
-      vanSidebar: this
-    };
-  },
-
-  data() {
-    return {
-      items: []
-    };
-  },
-
   render(h) {
     return <div class={[bem(), 'van-hairline--top-bottom']}>{this.slots()}</div>;
   }