Fix polkit keyfile backend

[dilyn-corner]

Thanks to the work done by solus, we have the ability to no longer require an entire javascript engine for a simple permissions framework. This is excellent, because it allows us to no longer require mozjs. Unfortunately, from everything I know of C, the code used for this keyfile backend is gross and bad. Ideally, we would simply clean it up. But I do not have the requisite knowledge of C to implement this (I don't even know enough to be dangerous).
As it stands, we need a single ifdef to remove the innetgr requirement imposed by this line. Assuming we can resolve this, we can drop the (very bad, from what I can gather) patch to musl.

If anybody can fix this small problem (or ideally, rewrite the entire policy backend solus is using), that would be a fantastic contribution to the project. In the mean time, I will be learning C.