chore: delete obsolete files, packages, imports and polyfills

src/main.js

@@ -1,12 +1,3 @@
-// The Vue build version to load with the `import` command
-// (runtime-only or standalone) has been set in webpack.base.conf with an alias.
-
-import 'core-js/es6/promise'
-import 'core-js/es6/string'
-import 'core-js/es7/array'
-import '@babel/polyfill'
-
-// import cssVars from 'css-vars-ponyfill'
 import Vue from 'vue'
 import App from './App'
 import router from './router'
@@ -14,7 +5,7 @@ import router from './router'
 import { CIconPlugin } from '@coreui/icons/vue'
 import { iconsSet } from './assets/icons/icons.js'
 
-import CoreuiVue from '@coreui/vue'
+import CoreuiVue from '@coreui/vue/src'
 
 Vue.config.performance = true
 Vue.use(CoreuiVue)