fix 1kN thruster suicide burn calc

[lamont-granquist]

i'm not sure if real fuels changed its API so that this no longer works
correctly or if it was not correct in the first place -- but this
definitely gets minthrust/maxthrust very wrong for the 1kN thruster
in realism overhaul / real fuels.

also applied the thrust limiter w/o the ullage clipping to zero to the
max thrust, which is what i thought this problem was going to be in the
first place -- this still looks like more correct code here, but wasn't
the root of the bug i was seeing in the suicide calcs.

[lamont-granquist]

@sarbian do you recall the use case you were trying to fix with the code i backed out here? it definitely causes issues now, but i can't guess at what you were trying to fix...

[sarbian]

I think the comment is clear "RealFuels engines reports as operational even when they are shutdown"
The engine report(ed) isOperational true even when not ignited.

I guess this is not longer the case ?

[lamont-granquist]

well, shutdown RF engines are not operational, so yes no longer the case?

but there's other conditions where an engine which is activated could be failed: vapor in the fuel lines, out of ignitions, Agathorn strikes again, etc.

but those conditions should be addressed via baking in better integration with RF: https://github.com/MuMech/MechJeb2/blob/master/MechJeb2/VesselState.cs#L1232-L1254

could probably put that into a PartExtensions for isEngineReallyOperational() that checked for vapor, ignitions, and Agathornage and get better code reuse out of that...