Resolve warning messages.

Problem/Motivation

Getting the following warning messages when using Disqus Comments.

Warning: Use of undefined constant DISQUS_API_NO_ACTION - assumed 'DISQUS_API_NO_ACTION' (this will throw an Error in a future version of PHP) in Drupal\disqus\Form\DisqusSettingsForm->buildForm() (line 191 of /app/web/modules/contrib/disqus/src/Form/DisqusSettingsForm.php)

Warning: Use of undefined constant DISQUS_API_CLOSE - assumed 'DISQUS_API_CLOSE' (this will throw an Error in a future version of PHP) in Drupal\disqus\Form\DisqusSettingsForm->buildForm() (line 192 of /app/web/modules/contrib/disqus/src/Form/DisqusSettingsForm.php)

Warning: Use of undefined constant DISQUS_API_REMOVE - assumed 'DISQUS_API_REMOVE' (this will throw an Error in a future version of PHP) in Drupal\disqus\Form\DisqusSettingsForm->buildForm() (line 193 of /app/web/modules/contrib/disqus/src/Form/DisqusSettingsForm.php)

Steps to reproduce

Go to Disqus configurations, save your configurations and the following warning messages will be logged in the DBLog.