chore($core): remove redundant code

Author: ulivz

packages/@vuepress/core/lib/internal-plugins/routes.js

@@ -16,8 +16,6 @@ function importCode () {
   return `
 import { injectComponentOption, ensureAsyncComponentsLoaded } from '@app/util'
 import rootMixins from '@internal/root-mixins'
-import layoutComponents from '@internal/layout-components'
-import pageComponents from '@internal/page-components'
 import LayoutDistributor from '@app/components/LayoutDistributor.vue'
 
 injectComponentOption(LayoutDistributor, 'mixins', rootMixins)