db: remove tag_aliases.post_count column.

This was only used in autocomplete, but it was unnecessary here because
we could already get the post count from the tags table.

app/models/tag.rb

@@ -895,7 +895,7 @@ class Tag < ApplicationRecord
       q
     end
 
-    def names_matches_with_aliases(name, limit: 10)
+    def names_matches_with_aliases(name, limit)
       name = normalize_name(name)
       wildcard_name = name + '*'
 
@@ -907,8 +907,8 @@ class Tag < ApplicationRecord
         .where("tag_aliases.antecedent_name LIKE ? ESCAPE E'\\\\'", wildcard_name.to_escaped_for_sql_like)
         .active
         .where("tags.name NOT LIKE ? ESCAPE E'\\\\'", wildcard_name.to_escaped_for_sql_like)
-        .where("tag_aliases.post_count > 0")
-        .order("tag_aliases.post_count desc")
+        .where("tags.post_count > 0")
+        .order("tags.post_count desc")
         .limit(limit * 2) # Get extra records in case some duplicates get filtered out.
 
       sql_query = "((#{query1.to_sql}) UNION ALL (#{query2.to_sql})) AS unioned_query"

app/models/tag_alias.rb

@@ -64,7 +64,7 @@ class TagAlias < TagRelationship
         update_posts
         forum_updater.update(approval_message(approver), "APPROVED") if update_topic
         rename_wiki_and_artist
-        update(status: "active", post_count: consequent_tag.post_count)
+        update(status: "active")
       end
     rescue Exception => e
       if tries < 5
@@ -183,10 +183,6 @@ class TagAlias < TagRelationship
     end
   end
 
-  def self.update_cached_post_counts_for_all
-    execute_sql("UPDATE tag_aliases SET post_count = tags.post_count FROM tags WHERE tags.name = tag_aliases.consequent_name")
-  end
-
   def create_mod_action
     alias_desc = %Q("tag alias ##{id}":[#{Rails.application.routes.url_helpers.tag_alias_path(self)}]: [[#{antecedent_name}]] -> [[#{consequent_name}]])