Remove unused useCDN field from sample config.

Author: johnjcamilleri

server-config.sample.js

@@ -2,7 +2,6 @@
 module.exports = {
   baseURL: '',
   fullBaseURL: 'http://localhost:3000',
-  useCDN: false,
   maintenanceMode: false, // put entire site down
   gabraURL: 'http://mlrs.research.um.edu.mt/resources/gabra',
   salt: '',