Add a gun-less variant of mansion safe item group and use it in the resort.

[kevingranade]

Summary

None

Purpose of change

While tracking down the source of some excessively common gun spawns I found that a ton of guns were spawning in the safe deposit boxes in the resort. Looks like "mansion_safe" is being used as a standin for "rich people stuff".

Describe the solution

Add a variant of the mansion_safe item group without guns and apply it to the resort.

Describe alternatives you've considered

There could be a special gun lockup placement as well (with much smaller numbers of guns).
The mansion_safe group isn't really a great match for this kind of thing and a replacement would be good, but this was the minimal change to fix the immediate problem I was having.

Testing

Generated some resorts and no guns, yay.