Revert "set localized date format for jquery ui datepicker, fixes #5507"

This reverts commit b60aa4fa.

resources/assets/javascripts/studip-ui.js

@@ -603,7 +603,7 @@ import RestrictedDatesHelper from './lib/RestrictedDatesHelper';
                 $gettext('Sa')
             ],
             weekHeader: $gettext('Wo'),
-            dateFormat: String.locale === 'en-GB' ? 'mm/dd/yy' : 'dd.mm.yy',
+            dateFormat: 'dd.mm.yy',
             firstDay: 1,
             isRTL: false,
             showMonthAfterYear: false,