MDL-64525 comments: Should not be able to delete frozen comments

Before this change in a frozen context a user would be able to delete
their own comments.

After this change a user will only be able to delete their own comments
if they still have the capability to post new comments or the capability
to delete comments from any user.

comment/classes/external.php

@@ -337,7 +337,7 @@ class core_comment_external extends external_api {
             $args->area      = $commentrecord->commentarea;
             $manager = new comment($args);
 
-            if ($commentrecord->userid != $USER->id && !$manager->can_delete($commentrecord->id)) {
+            if (!$manager->can_delete($commentrecord)) {
                 throw new comment_exception('nopermissiontodelentry');
             }