Remove leftover from r1225, #1484316.

program/js/app.js

@@ -132,7 +132,6 @@ function rcube_webmail()
           this.message_list.addEventListener('dblclick', function(o){ p.msglist_dbl_click(o); });
           this.message_list.addEventListener('keypress', function(o){ p.msglist_keypress(o); });
           this.message_list.addEventListener('select', function(o){ p.msglist_select(o); });
-          this.message_list.addEventListener('dragstart', function(o){ p.drag_active = true; });
           this.message_list.addEventListener('dragstart', function(o){ p.drag_active = true; if (p.preview_timer) clearTimeout(p.preview_timer); });
           this.message_list.addEventListener('dragend', function(o){ p.drag_active = false; });