Remove unused help page entry point

When we introduced (3d036617) the help entry point, it was likely to
render a list of icons within our documentation. We are not doing that,
so we can get rid of it.

app/assets/javascripts/help/help.js

-// We will render the icons list here
-
-import $ from 'jquery';
-
-export default () => {
-  if ($('#user-content-gitlab-icons').length > 0) {
-    const $iconsHeader = $('#user-content-gitlab-icons');
-    const $iconsList = $('<div id="iconsList">ICONS</div>');
-    $($iconsList).insertAfter($iconsHeader.parent());
-  }
-};

app/assets/javascripts/pages/help/show/index.js

-import initHelp from '~/help/help';
-
-document.addEventListener('DOMContentLoaded', initHelp);