Removing an Add Player event shouldn't remove the player completely

[alopezlago]

1. Create a game with a substitute player (i.e. non-starter)
2. Add them to the game
3. Remove them from the game through the event log

Expected:
The player is still there as a substitute
Actual:
The player is completely gone

This can also happen if someone leaves the game and then joins back in later, and you delete that join event.

[alopezlago]

This requires updating removeNewPlayer to not change the players collection. It also needs a cycle index so we don't remove events from before the addition.