Remove leftover sub-tag support.

app/assets/javascripts/discourse/models/topic.js.coffee

@@ -69,13 +69,6 @@ Discourse.Topic = Discourse.Model.extend Discourse.Presence,
 
   ).property('new_posts', 'id')
 
-  displayTitle: (->
-    return null unless @get('title')
-    return @get('title') unless @get('category')
-    matches = @get('title').match(/^([a-zA-Z0-9]+\: )?(.*)/)
-    return matches[2]
-  ).property('title')
-
   # The coldmap class for the age of the topic
   ageCold: (->
     return unless lastPost = @get('last_posted_at')

app/assets/javascripts/discourse/templates/topic.js.handlebars

@@ -17,7 +17,7 @@
             <h1>
               {{#if view.topic.title}}
                 {{view Discourse.TopicStatusView topicBinding="view.topic"}}
-                <a href='{{unbound view.topic.url}}'>{{unbound view.topic.displayTitle}}</a>
+                <a href='{{unbound view.topic.url}}'>{{unbound view.topic.title}}</a>
               {{else}}
                 {{#if view.topic.missing}}
                   {{i18n topic.not_found.title}}

app/assets/javascripts/discourse/templates/topic_extra_info.js.handlebars

@@ -5,7 +5,7 @@
 <h1>
 {{#if view.topic.title}}
   {{view Discourse.TopicStatusView topicBinding="view.topic"}}
-  <a class='topic-link' href='{{unbound view.topic.url}}'>{{view Discourse.AutoSizedTextView tagName="span" class="auto-sizer" contentBinding="view.topic.displayTitle"}}</a>
+  <a class='topic-link' href='{{unbound view.topic.url}}'>{{view Discourse.AutoSizedTextView tagName="span" class="auto-sizer" contentBinding="view.topic.title"}}</a>
 {{else}}
   {{#if view.topic.missing}}
     {{i18n topic.not_found.title}}