Activision has been purging licensed games from online stores recently, taking games off of the market that have been around for a while. The trend started very recently with the removal of Spider Man licensed games, and has been continuing today. The trend was continued with Platinum's Teenage Mutant Ninja Turtles games today, which were removed from stores in just the same way.
Activision hasn't yet given a reason for these skins disappearing, but it's a shame for anyone who hasn't played them yet. Of course, retail copies of the games are still in stores and pre-existing digital copies are still totally valid to play with.
At this point, the real question is why these takedowns are happening. It's not normal for a company to just take something off of the market - we can only guess that it's due to an upcoming deal that might complicate Activision's rights to these franchises. For example, a new Spider Man game is on its way to PS4 in the near future.