Fixes #2553 and #2533

- Fixes the away map dead slime spawner. Previously, it would spawn two
dead slimes that had living icons. Now it spawns one slime with a dead
icon.  These issues are fixed by adding a check for existing slimes at
the spawner's location before spawning a slime, and killing the spawned
slime via adjustToxLoss() instead of death(). Death() doesn't give the
slime a dead icon for some reason.

- Fixes the away map dead AI spawner. Previously, it spawned a dead AI
that showed on the PDA messenger from roundstart, made the AI status
displays on the station show the BSoD, and displayed its laws in the
round-end report. These issues are fixed by setting the spawned AI's PDA
toggle to 1, changing the status displays back to blank after the AI
dies and removing the dead AI from the moblist so it isn't shown at the
end of the game.

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