Update Kiwi -- remove unused code, update from Mimiktaz, include KB2871997 Fix

This code contains a stack of changes pulled from the Mimikatz repo. It doesn't have all of them, but it does have up to and including the important fix for `KB2871997`, which means the extension now works again on systems with this patch (thanks to @gentilkiwi of course).

There'll be more to come down the track, but this is worthy of the PR by itself.