DEV: TODO followups (#18936)

* Remove old bookmark column ignores to follow up b22450c7a8
* Change some group site setting checks to use the _map helper
* Remove old secure_media helper stub for chat
* Change attr_accessor to attr_reader for preloaded_custom_fields to follow up 70af45055a

db/post_migrate/20221108032233_drop_old_bookmark_columns_v2.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require 'migration/column_dropper'
+
+class DropOldBookmarkColumnsV2 < ActiveRecord::Migration[7.0]
+  DROPPED_COLUMNS ||= {
+    bookmarks: %i{
+      post_id
+      for_topic
+    }
+  }
+
+  def up
+    DROPPED_COLUMNS.each do |table, columns|
+      Migration::ColumnDropper.execute_drop(table, columns)
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end