models: remove hack to ignore tsvector columns.

Previously we overrode `ActiveRecord::Base#columns` to make it ignore
tsvector columns so they wouldn't show up in API responses. These
columns have been removed, so this is no longer necessary.

app/models/application_record.rb

@@ -173,14 +173,6 @@ class ApplicationRecord < ActiveRecord::Base
     end
   end
 
-  concerning :PostgresExtensions do
-    class_methods do
-      def columns(*params)
-        super.reject {|x| x.sql_type == "tsvector"}
-      end
-    end
-  end
-
   concerning :UserMethods do
     class_methods do
       def belongs_to_updater(**options)