Block extra costume slots on ranked mode#696

When a player queues into ranked with an iso modded using m-ex, they can currently use skins in extra costume slots. This causes a few issues:

1. A player not in the know will be confused as to which character their opponent is using and may strike to a stage they’d otherwise not go to, or they may even press escape and forfeit the set after assuming slippi is bugged.
2. Due to how Melee loadinjg the neutral costume as a failsafe when the costume slot it tries to load doesn’t exist, one could potentially force their opponent to play against their own skin (which shouldn’t usually happen on ranked mode).

I remember Fizzi tweeting that it was impossible to distinguish between a vanilla and a modded iso when it comes to accessing ranked, but would it be possible to just stop players from selecting costume slots that aren’t in the vanilla game, similar to how it blocks custom characters? This would probably be enough to prevent the issues I mentioned above.