What's needed here is a "naming and shaming" effort. Make a public directory of bad PHP tutorials/references/etc., with the names of the people and companies who wrote and host them prominently attached. Maybe even give them a score, based on how frequently cited/linked to their bad advice has become, or how many pieces of it they've proffered. Then only take them off the list when the documents are cleaned up or removed.
If you're a professional PHP developer or a company that builds on PHP, it would be very embarrassing to find yourself prominently featured on such a list. Which would create an incentive for those people to clean up their work so they can get off it.
As things stand currently, publishing outdated and dangerous information costs the publisher nothing, so they see no reason to stop doing it. Create a cost by attaching reputational damage to the act, and you create a reason for them to stop.