Exclude removed comments from "last comment" link

The "last comment posted" link in the sidebar on a topic's comments page
was still considering removed comments, so if the last comment in a
topic was removed it would link to that one. That's not very useful for
anyone, so this excludes removed comments the same way that deleted ones
were already excluded.

tildes/tildes/models/comment/comment_tree.py

@@ -181,9 +181,9 @@ class CommentTree:
 
     @property
     def most_recent_comment(self) -> Optional[Comment]:
-        """Return the most recent non-deleted Comment in the tree."""
+        """Return the most recent Comment in the tree (excluding deleted/removed)."""
         for comment in reversed(self.comments):
-            if not comment.is_deleted:
+            if not (comment.is_deleted or comment.is_removed):
                 return comment
 
         return None

tildes/tildes/templates/topic.jinja2

@@ -326,7 +326,7 @@
     <dt>Last comment posted</dt>
     <dd>
       <a href="{{ comments.most_recent_comment.permalink }}" data-js-hide-sidebar-no-preventdefault>
-        {{ adaptive_date_responsive(topic.last_activity_time) }}
+        {{ adaptive_date_responsive(comments.most_recent_comment.created_time) }}
       </a>
     </dd>
   {% else %}