Remove an unnecessary null check.

If OnSave is called, Instance cannot be null because it is guaranteed that
Awake will have been called.
Move the chute warning flag to the scenario.

This makes the setting "global" (ie for all difficulty settings) and
actually save properly without needing to hack the config files. It also
has the effect of making the setting per-save, which I consider to be a
good thing as it will serve as a reminder.
Visually separate the chute toggle from the other settings.

This makes it clear that the chute warning toggle is not part of the
difficulty settings.