Nuke disk as standard steal objective

Replaced pinpointer steal objective with the nuke disk.

The disk is only prevented from z-level border transitions and teleportation. It can still travel via shuttles and pods.

It would be an interesting steal objective as it can be pinpointed, as well as the restriction of changing z-levels.

It would also stop the awkward meta where the nuke disk can be completely disregarded, left in the middle of hallways, because enough time had passed to be sure it was not a nuke round.

The pinpointer objective was only added in the first place because we thought the nuke disk couldn't be used.