Rename certificate issue events (#675)

Author: mdjnelson

classes/event/certificate_deleted.php

@@ -122,8 +122,6 @@
 $string['eventtemplatecreated'] = 'Custom certificate template created';
 $string['eventtemplatedeleted'] = 'Custom certificate template deleted';
 $string['eventtemplateupdated'] = 'Custom certificate template updated';
-$string['eventcertificateupdated'] = 'Certificate updated';
-$string['eventcertificatedeleted'] = 'Certificate deleted';
 $string['exampledatawarning'] = 'Some of these values may just be an example to ensure positioning of the elements is possible.';
 $string['font'] = 'Font';
 $string['font_help'] = 'The font used when generating this element.';