remove vestigial onsubmit event trigger

app/views/shared/issuable/_search_bar.html.haml

@@ -125,10 +125,6 @@
   new MilestoneSelect();
   new IssueStatusSelect();
   new SubscriptionSelect();
-  $('form.filter-form').on('submit', function (event) {
-    event.preventDefault();
-    Turbolinks.visit(this.action + '&' + $(this).serialize());
-  });
   $(document).off('page:restore').on('page:restore', function (event) {
     if (gl.FilteredSearchManager) {