Restrict NotificationSetting#event_enabled? method to only attributes

What does this MR do?

Restrict method to only attributes

Rather than having the ability to call any method on this class

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

All events should be DB columns, including the new_epic attribute (EE only). ee/spec/models/ee/notification_setting_spec.rb and spec/models/notification_setting_spec.rb have enough coverage here.