I don't recall it ever being important that the audience knew who Carol was. What was important was that Rogue was a villain who went too far and regretted it and that she had someone else's mind trapped in her head which was why she needed Xavier's help (and why she was constantly forced to remember her villainous past).
The thing is, nowadays most adaptations (and even the comics themselves) tend to ignore Rogue being an outright villain once who only became heroic because Carol's heroic traits basically took over Rogue's mind and just act like she always had heroic traits and this incident is what made her reconsider her life after being "led astray" by Mystique.
So that means there's even less reason to waste Carol like this, because when Rogue is used in the movies odds are she'll already be good and there'll be no point in having Carol's mind be the reason she turns.