Remove usage of `baseInputs` to avoid confusion?

[martin-braun]

I'm coming from #87. Reading through Nix Pills, I can still find numerous references to baseInputs that caused great confusion on my end as a newcomer when transitioning to mkDerivation, please take the time to get rid of things that aren't used in the mkDerivation at all, because you end up in false assumptions from the things you learned previously.

Unlearning is significantly harder than learning.

[YievCkim]

Yes the sentence suggests that's an alternative but the code without this change doesn't work. It would be much better to insist on alternatives: merge buildInputs vs keep them in two attributes.