This fixes a bug where if you died after activating a teleporter prompt
and then respawned in the same room as the teleporter, the teleporter
prompt would go away. Which would be very annoying if you wanted to, you
know, teleport.
You don't even have to R-press to make this happen. "Level Complete!"
and Energize are two teleporter rooms in the main game that have hazards
in them.
I see no reason to set game.activetele to false when dying. For one, it
gets set to false during a gotorom anyway. For another, I couldn't get
the game to activate the teleport prompt in a room without a teleporter
in my testing, mostly because when you touch a teleporter, your
checkpoint is set to that teleporter, so you can't R-press to go to
another room and carry over the teleport prompt.