Remove roundstart runtimes

Having runtimes on roundstart is pretty sad so I fixed them
N2O floors were simple, added a check so they don't try to dick with their non-existent air datum
The others were more  _interesting_ and warrant some explanation so hopefully they don't happen again.

<b>tl;dr turfs are changelings, mob code is garbage, and people think its ok to avoid fixing runtimes for a year </b>

Mining turfs' ```New()``` was calling one of their procs after a ```spawn()```.
The problem is, during that spawn, they were actually getting _deleted and replaced with a different turf_ (a mining room turf, a ```/simulated/wall``` instead of an ```/unsimulated/floor```).
When turfs get deleted, their running procs aren't killed or have ```src``` set to null.
Instead, the procs' ```src``` is set to the new turf and they continue running like nothing's wrong.
After coming back from the ```spawn()```, ```New()``` was trying to call one of its turf's procs, only to find that it had been _replaced by an impostor!_ :fearful:
Fixed by removing the ```spawn()``` (which was added in https://github.com/d3athrow/vgstation13/commit/52c900520ccc390afc9056c1109b8745317b1a62 in 2011 _with no explanation of course_ :trollface:)

Humans' ```New()``` was calling their ```set_species()```, which was very crappy.
It was crashing due to a runtime when the space russian corpse was created and attempted to get a species from the global list.
Problem is, it was initializing before ```/world```, and ```/world/New()``` actually builds its species list.
Easily fixed. But now the server _didn't even start_.
That's because the runtime in ```set_species()``` was causing ```New()``` to crash before finishing.
When ```New()``` didn't crash, it went on to call a proc that eventually _attempted to divide by zero_.
That's because it was dividing by a value it got from a global list. An uninitialized global list. :disappointed:
Fixed that too (by building the lists when they're actually needed and cleaning up the species setting)
This shit was introduced in https://github.com/d3athrow/vgstation13/commit/65f4751b60f45a2665dee80b76a4bcf983ad8534 and https://github.com/d3athrow/vgstation13/commit/27e1c5e869f77f1b9ece1ae09fda18069b5f699b and https://github.com/d3athrow/vgstation13/commit/2b77203275a03f765bb1257a96e1c85204ebc74f (all bay ports)