change random event antag spawns to be based on dead players instead of dead antags

[pali6]

Unless I'm mistaken currently they're based on both dead antags and dead players. Iirc basically the event triggers if there are too few antags or too many dress people.

EDIT: Yep. On classic it triggers if less than 10% of original antags are alive or if more than 30% of crew is dead. On RP the 10% is replaced by 4%.