Colocate alert styles (#9117)

ui/app/components/app/index.scss

@@ -1,5 +1,6 @@
 @import 'account-menu/index';
 @import 'add-token-button/index';
+@import '../ui/alert/index';
 @import 'alerts/alerts';
 @import 'app-header/index';
 @import 'asset-list-item/asset-list-item';

ui/app/css/itcss/components/index.scss

@@ -7,7 +7,6 @@
 @import './footer';
 @import './network';
 @import './modal';
-@import './alert';
 @import './newui-sections';
 @import './account-dropdown';
 @import './send';