Revert "Commit to using Yarn over NPM"

This reverts commit dd6a2600e7.

app/assets/javascripts/application.js

@@ -55,7 +55,7 @@
 //= require bootstrap-select
 //= require osem-survey
 //= require pagy
-//= require @fullcalendar/common/main.js
+//= require fullcalendar-scheduler/main.js
 
 $(document).ready(function() {
     $('a[disabled=disabled]').click(function(event){

app/assets/stylesheets/application.css

@@ -26,4 +26,6 @@
  *= require osem-navbar
  *= require mastodon
  *= require conferences
+
+ *= require fullcalendar-scheduler/main.css
 */