Disable registration tokens for all instances except GitLab.com

See more at Replace FF with settings migration in runner to... (!122316 - merged) and https://docs.gitlab.com/ee/architecture/blueprints/runner_tokens

To encourage users to migrate to the new architecture, we update ApplicationSetting.allow_runner_registration_token = false for every instance except gitlab.com.

Users can still flip this setting back to true until %18.0.