Breaks save compat because it adds new fields to `Flight` that have no
constant default. Removing all of our other save compat at the same
time.
Note that player flights with a divert point will have a nav point for
their actual landing point. This is because we place the divert point
last, and DCS won't let us have a land point anywhere but the final
waypoint. It would allow a LandingReFuAr point, but they're only
generated for player flights anyway so it doesn't really matter.
Fixes https://github.com/Khopa/dcs_liberation/issues/342