refactor: removed dark theme

Author: PKulkoRaccoonGang

env.config.js

@@ -7,19 +7,13 @@ module.exports = {
     },
     defaults: {
       light: 'light',
-      dark: 'dark',
     },
     variants: {
       light: {
         urls: {
           default: 'https://cdn.jsdelivr.net/npm/@openedx/paragon@alpha/dist/light.min.css',
         },
       },
-      dark: {
-        urls: {
-          default: 'https://cdn.jsdelivr.net/npm/@edx/brand-edx.org@alpha/dist/light.min.css',
-        },
-      },
     },
   },
 };