We switched to PHPDataSets already but didn't migrate all usages. This commit now migrates all usages left behind.
Past data is now removed again. A test ensures the functionality. Data is no longer marked as deleted but is actually deleted. Relates: #9543
Adjust existing code base to not use hardcoded file path. Instead use info from database and check all files which have references to event objects. Also add test to cover feature.
