Implement core_privacy for report completion

Testing can be completed by running the attached testwithmanager.php script (see ---- MDL-61571 ---- for the original script location) in the Moodle root folder. Make sure you've purged the cache (php admin/cli/purge_caches.php), before running testwithmanager.php. Check that report_completion is compliant Check that report_completion is a null provider Check that the null reason is valid You should receive a script output like: Testing the compliant plugins:   .....   == report_completion (report_completion\privacy\provider) == Claims not to store any data with reason: 'The Course completion report only shows data stored in other locations.'