PERF: stop adding more topics to search when not needed

The logic of adding additional search results does not seem to be
needed anymore.

It appears to be a relic of an old implementation.

This saves an entire search query for every search made.

lib/search.rb

@@ -21,12 +21,6 @@ class Search
     50
   end
 
-  # Sometimes we want more topics than are returned due to exclusion of dupes. This is the
-  # factor of extra results we'll ask for.
-  def self.burst_factor
-    3
-  end
-
   def self.facets
     %w(topic category user private_messages tags all_topics)
   end
@@ -710,30 +704,12 @@ class Search
       topic_search
     end
 
-    add_more_topics_if_expected
     @results
   rescue ActiveRecord::StatementInvalid
     # In the event of a PG:Error return nothing, it is likely they used a foreign language whose
     # locale is not supported by postgres
   end
 
-  # Add more topics if we expected them
-  def add_more_topics_if_expected
-    expected_topics = 0
-    expected_topics = Search.facets.size unless @results.type_filter.present?
-    expected_topics = Search.per_facet * Search.facets.size if @results.type_filter == 'topic'
-    expected_topics -= @results.posts.length
-    if expected_topics > 0
-      extra_posts = posts_query(expected_topics * Search.burst_factor)
-      extra_posts = extra_posts.where("posts.topic_id NOT in (?)", @results.posts.map(&:topic_id)) if @results.posts.present?
-      extra_posts.each do |post|
-        @results.add(post)
-        expected_topics -= 1
-        break if expected_topics == 0
-      end
-    end
-  end
-
   # If we're searching for a single topic
   def single_topic(id)
     if @opts[:restrict_to_archetype].present?