[Site] Remove Swup dependencies

Author: Kocal

ux.symfony.com/importmap.php

@@ -167,9 +167,6 @@
     'path-to-regexp' => [
         'version' => '6.2.1',
     ],
-    '@swup/theme' => [
-        'version' => '2.1.0',
-    ],
     '@kurkle/color' => [
         'version' => '0.3.2',
     ],