Fixed czech translation for timeago (#4622)

When czech language is set, browser throws 404 Not Found error on jquery.timeago.cz.js
Thats because translation file were renamed 
81f072ebb2
https://github.com/NodeBB/NodeBB/blob/master/public/vendor/jquery/timeago/locales/jquery.timeago.cs.js

so that cs->cz override is no needed anymore.

public/src/modules/translator.js

@@ -72,10 +72,6 @@
 				languageCode = 'en';
 				break;
 
-			case 'cs':
-				languageCode = 'cz';
-				break;
-
 			case 'fa_IR':
 				languageCode = 'fa';
 				break;