fix(admin): remove NotFound component

The NotFound component was removed in @strapi/helper-plugin and was not actually used

fix #339

Author: sargreal

plugin/admin/src/pages/App/index.js

@@ -7,7 +7,6 @@
 
 import React from 'react'
 import { Switch, Route } from 'react-router-dom'
-import { NotFound } from '@strapi/helper-plugin'
 import pluginId from '../../pluginId'
 import HomePage from '../HomePage'
 
@@ -16,7 +15,6 @@ const App = () => {
     <div>
       <Switch>
         <Route path={`/plugins/${pluginId}`} component={HomePage} exact />
-        <Route component={NotFound} />
       </Switch>
     </div>
   )