Revert using Embedly to canonicalize link topics

This isn't working very well in a lot of cases, shouldn't be used until
I've got some workarounds for a lot of the issues that I'm finding.

This reverts commit 369f273f8e.

tildes/consumers/topic_embedly_extractor.py

@@ -66,10 +66,6 @@ class TopicEmbedlyExtractor(PgsqlQueueConsumer):
 
             self.db_session.add(result)
 
-        # update the topic's link if embedly says the final url is different
-        if topic.link != result.data["url"]:
-            topic.link = result.data["url"]
-
         new_metadata = EmbedlyScraper.get_metadata_from_result(result)
 
         if new_metadata: