Remove rounded O2 in air

To quote Linus, gentle as always:

 Stuff like this is just BS.

 Don't do it. You already fixed the bug with matching gas change events,
 so adding this idiotic workaround no longer fixes anything, and its
 confusing and actively misleading.

 It's not even percent. It's still permille, just rounded. So it's a
 nonsensical number and a misleading name. Just delete it as the abortion
 it is. It is only going to cause more problems later.

 Just use the correct value.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>