Named views without definePage should not generate an import in auto-routes

[posva]

This should be the better fix for #338

currently, the playground generates this code:

import _definePage_default_0 from '/Users/posva/unplugin-vue-router/playground/src/pages/index.vue?definePage&vue'
import _definePage_named_1 from '/Users/posva/unplugin-vue-router/playground/src/pages/index@named.vue?definePage&vue'
import { _mergeRouteRecord } from 'unplugin-vue-router/runtime'


export const routes = [
  _mergeRouteRecord(
  {
    path: '/',
    name: 'home',
    components: {
      'default': () => import('/Users/posva/unplugin-vue-router/playground/src/pages/index.vue'),
      'named': () => import('/Users/posva/unplugin-vue-router/playground/src/pages/index@named.vue')
    },
    /* no children */
  },
  _definePage_default_0,
_definePage_named_1
  ),
// ...

Since index@named.vue doesn't have a definePage() inside it, it would be better if it was skipped completely