remove unnecessary DOM Content Loaded Event Listener

app/assets/javascripts/behaviors/index.js

@@ -25,8 +25,7 @@ initPageShortcuts();
 initCollapseSidebarOnWindowResize();
 initSelect2Dropdowns();
 
-document.addEventListener('DOMContentLoaded', () => {
-  window.requestIdleCallback(
+window.requestIdleCallback(
   () => {
     // Check if we have to Load GFM Input
     const $gfmInputs = $('.js-gfm-input:not(.js-gfm-input-initialized)');
@@ -39,5 +38,4 @@ document.addEventListener('DOMContentLoaded', () => {
     }
   },
   { timeout: 500 },
-  );
-});
+);