Immersion tweaks

WATERPROOF now no longer helps if you're in deep water.  In practice,
this nerfs hazmat gear slightly.  However, I don't think it's designed
for swimming, so am not gonna fret about water getting in the seams of
an airtight suit.
Make the delete world option delete worlds indead of reseting them

Fixes #5506
Merge branch 'Waterproofing' of github.com:KA101/Cataclysm-DDA
Merge branch 'delete-world' of github.com:fergus-dall/Cataclysm-DDA