Sorry what's decanonize?
Essentially it would mean that as a Star Wars viewer you would basically forget these films existed. They would not be part of the official lore. The bible, for instance, has had many books removed from it over time, and they are no longer part of the official canon of the bible and therefore aren't included in the King James version of the bible. They still were at one point in time part of the original text, but time (or voting) has removed them from what would be considered "official." Sorry to use such a significant piece of history or literature as my example, but you can see then the power that decanonization can have on history, even for something as far reaching as a religious testament.