posts: fix search queries not being logged to NewRelic in some cases (#4900)

Fix the /posts index controller not logging the normalized search query
to NewRelic when the search failed, either because of a tag limit error,
a search timeout, or a RSS feed rate limit error.

Also don't log the number of search results when it's an API request or
failed search. This is to avoid doing a potentially slow full post count
when it's not otherwise needed.

app/logical/post_query_builder.rb

@@ -968,7 +968,7 @@ class PostQueryBuilder
 
   concerning :CountMethods do
     def post_count
-      fast_count
+      @post_count ||= fast_count
     end
 
     # Return an estimate of the number of posts returned by the search.  By

app/logical/post_sets/post.rb

@@ -137,24 +137,6 @@ module PostSets
       end
     end
 
-    def search_stats
-      {
-        query: normalized_query.to_s,
-        count: post_count,
-        page: current_page,
-        limit: per_page,
-        term_count: normalized_query.terms.count,
-        tag_count: normalized_query.tags.count,
-        metatag_count: normalized_query.metatags.count,
-        censored_posts: censored_posts.count,
-        hidden_posts: hidden_posts.count,
-      }
-    end
-
-    def log!
-      DanbooruLogger.add_attributes("search", search_stats)
-    end
-
     concerning :TagListMethods do
       def related_tags
         if query.is_wildcard_search?