Fixes Soul Scythe being able to get to Centcom by moving down on the bottom Z-level (#71171)
Fixes Soul Scythe being able to get to Centcom by moving down on the bottom Z-level (#71171)

## About The Pull Request

`/obj/item/soulscythe/relaymove()` was using `get_step()` which doesn't
understand our multi-z system and was happily trying to move Z - 1 which
is Centcom. I'm still not really sure I understand why move() allowed
the scythe to just move right through the floor in this case, I think
moving to turfs with `density = 0` is also behaving strangely and just
skipping some checks that should keep it from moving through the floor,
but to be honest I don't fully understand the move chain and just
changing to `get_step_multiz()` at least keeps the scythe from going to
Z-levels it shouldn't.
## Why It's Good For The Game

Whilst it is fun for the scythe to go on an adventure to forbidden
Z-levels, admins probably don't appreciate these adventures so much.
## Changelog
:cl: VexingRaven
fix: Soul Scythes can no longer phase through the floor into Centcom.
/:cl:
tgstation/tgstation,tgstation/tgstation,Bawhoppen/-tg-station,Bawhoppen/-tg-station,tgstation/tgstation,Bawhoppen/-tg-station,tgstation/tgstation,Bawhoppen/-tg-station,Bawhoppen/-tg-station,tgstation/tgstation,tgstation/tgstation,tgstation/tgstation,Bawhoppen/-tg-station,Bawhoppen/-tg-station,Bawhoppen/-tg-station,tgstation/tgstation