RS-68/RS-68K Nozzle Ablator

[Capkirk123]

At the moment, the RS-68 engine simulates the use of ablative cooling by burning an amount of ablator along with fuel. Due to the mass-ratio sensitivity of hydrolox stages, the 1.1 tons of ablator burnt do make a significant difference in the performance of an RS-68-based stage.

However, the RS-68 has regen-cooled configs, which should not have ablator, but it is added anyway due to the inability of MEC to manipulate part resources on a per-config basis. This should probably be removed, and B9PS used instead to handle the presence of ablator (Specific to ROEngines, other parts configured as the RS-68 will probably need resolution also, but that's outside the scope of this issue).