Keep darkmode state in serverside session too. Fix darkmode state in egroupware iframes.

api/js/jsapi/egw_app.js

@@ -116,8 +116,6 @@ var EgwApp = /** @class */ (function () {
         this._fix_iFrameScrolling();
         if (this.egw && this.egw.is_popup()) {
             this._set_Window_title();
-            // apply theme mode
-            jQuery('html').attr('data-darkmode', egw.getSessionItem('api', 'darkmode') == '0' ? '0' : '1');
         }
         // Highlights the favorite based on initial list state
         this.highlight_favorite();