There was a Google Chrome extension to delete Facebook friends en masse, it's still available I believe. Personally, you're better off doing that manually or by using a preprogrammed auto-clicker to manually go about deleting your friends if it's too troublesome. Using the extension or any other way that immediately clears your friends by the bulk will definitely be picked up by FB. I mean suddenly delete all of your friends will do that anyway but it would be ruled somewhat less suspiciously if it happened over a span of a day or so. Best to exercise caution, regardless.
