Event registration breaks when CiviContribute isn't enabled
This seems closely related to #4492 (closed). I wonder where else this might arise?
Error: Class "Civi\Api4\LineItem" not found in CRM_Event_WorkflowMessage_EventOnlineReceipt->setParticipantID() (line 97 of /var/www/reg.wiscience.wisc.edu/web/sites/all/modules/civicrm/CRM/Event/WorkflowMessage/ParticipantTrait.php).