Revert "FIX: fallback to custom type for flags (#27961)" (#27962)

This reverts commit 7b6b7ca863.

app/models/flag.rb

@@ -1,6 +1,9 @@
 # frozen_string_literal: true
 
 class Flag < ActiveRecord::Base
+  # TODO(2025-01-15): krisk remove
+  self.ignored_columns = ["custom_type"]
+
   DEFAULT_VALID_APPLIES_TO = %w[Post Topic]
   MAX_SYSTEM_FLAG_ID = 1000
   MAX_NAME_LENGTH = 200
@@ -23,15 +26,6 @@ class Flag < ActiveRecord::Base
     Set.new(DEFAULT_VALID_APPLIES_TO | DiscoursePluginRegistry.flag_applies_to_types)
   end
 
-  # TODO(2025-01-15): krisk remove
-  def require_message
-    if ActiveRecord::Base.connection.column_exists?(:flags, :require_message)
-      super
-    else
-      self.custom_type
-    end
-  end
-
   def self.reset_flag_settings!
     # Flags are memoized for better performance. After the update, we need to reload them in all processes.
     PostActionType.reload_types