It's Wikipedia. Anyone can change the entries. Only solution is to create your own user account and alter it as you see fit, i.e. take out the 'non-canon' material and place it into its own section within the entry, clearly stating its context, e.g. create a heading called 'Winegardner Sequel Novels'.

Remove it altogether & someone else will just modify the main part with the Winegardner elements as if they appeared in the original novel or films. It's not through malice or opinion, just a certain ignorance or indifference to what more hardcore GF fans consider to be authentic.
Someone might read the entry on Tom Hagen after having read 'The Godfather's Revenge' and think, "OMG! They left out the bit where he drowns in the car! Better fix that up..."

Wikipedia is pretty much 100% democratic, so you either live with it or change it in such a way that you think the information is being presented correctly. Taking a stance on 'canon' isn't the way to go, best to just present all the facts in their proper contexts.