chore: delete unused import of shopping-cart example (#2156)

Author: ruochuan12

examples/composition/shopping-cart/app.js

@@ -1,7 +1,6 @@
 import { createApp } from 'vue'
 import App from './components/App.vue'
 import store from './store'
-import { currency } from './currency'
 
 const app = createApp(App)