DOC-3195: Remove outdated comments callback example for tinycomments in v6 documentation suite. (#3677)

* DOC-3195: Remove outdated comments callback example and related JavaScript code.

* DOC-3195: Update comments callback demo and add user avatars.

* Update modules/ROOT/examples/live-demos/comments-callback/index.js

Co-authored-by: tiny-ben-tran <ben.tran@tiny.cloud>

---------

Co-authored-by: tiny-ben-tran <ben.tran@tiny.cloud>

Author: kemister85

modules/ROOT/examples/live-demos/comments-callback/example.js

@@ -7,7 +7,7 @@ <h2>Welcome to Tiny Comments!</h2>
     <li>Type your comment into the text field at the bottom of the Comment sidebar.</li>
     <li>Click <strong>Comment</strong>.</li>
   </ol>
-  <p>Your comment is then attached to the text, exactly like this!</p>
+  <p>Your comment is <span class="mce-annotation tox-comment" data-mce-annotation-uid="mce-conversation_420304606321716900864126" data-mce-annotation="tinycomments">then</span> attached to the text, <span class="mce-annotation tox-comment" data-mce-annotation-uid="mce-conversation_19679600221621399703915" data-mce-annotation="tinycomments">exactly like this!</span></p>
   <p>If you want to take Tiny Comments for a test drive in your own environment, Tiny Comments is one of the premium plugins you can try for free for 14 days by signing up for a Tiny account. Make sure to check out our documentation as well.</p>
   <h2>A simple table to play with</h2>
   <table style="border-collapse: collapse; width: 100%;" border="1">