remove deprecated key prop in descriptionAddon (#6348)

Author: sookmax

.storybook/custom-addons/descriptions/register.js

@@ -19,8 +19,8 @@ addons.register(ADDON_ID, (api) => {
   addons.add(PANEL_ID, {
     type: types.PANEL,
     title: 'Description',
-    render: ({ active, key }) => (
-      <AddonPanel active={active} key={key}>
+    render: ({ active }) => (
+      <AddonPanel active={active}>
         <MyPanel />
       </AddonPanel>
     ),