Simplify pkg-config logic by removing the batch query

Could we consider just dropping the batch query completely? This was asked in https://github.com/haskell/cabal/pull/9134#issuecomment-1645351542 and https://github.com/haskell/cabal/pull/9134#issuecomment-1791857630. AFAICT all it gives us is a fairly small speedup on some systems, while doubling the time for anyone with any broken packages (which is common: #8930) and adding complexity.

(It would be even better if we cached results on a per-package basis, as in #9360.)

_Originally posted by @georgefst in https://github.com/haskell/cabal/issues/9391#issuecomment-1816366109_