Remove deprecated code from \Drupal\Core\Cron

The title needs to be more explicit. Every time I have read this I note that core/modules is not in a 'lib' directory. A positive statement of which files are include would be be better.

Turns out there was just 1 file

Random failure in migration unit test.

This should be ready for review now.

Thank you, naming looks good

Committed 1d6ca73 and pushed to 11.x. Thanks!

Automatically closed - issue fixed for 2 weeks with no activity.