[TASK] remove lastPublishedDate from transactional send journeys

[JoernBerkefeld]

looks like this is always set to "lastPublishedDate": "0001-01-01T00:00:00", even after the associated transactionalEmail was set to "Active".

My assumption is, this field gets updated only be the event-publish flow (used for multi-step journeys) and is not getting updated by the publish flow for transactionalEmail

we should strip it on journeys with status == "Published" and definitionType == "Transactional" if it is equal to "0001-01-01T00:00:00" (to make sure we do not strip it anymore in case SFMC ever fixes that gap.