Remove unix-2.8 patching for now

I originally patched these libraries in anticipation of GHC HEAD bundling the yet-to-be-released unix-2.8 instead of unix-2.7. However, since then HEAD has switched back to unix-2.7 and doesn't show any signs of going back to 2.8 any time soon. Keeping these patches around, therefore, is a bit wasteful since it results in more Cabal store cache misses without any benefits, since these libraries build on HEAD just fine. Until the need to actually adjust to unix-2.8 arises once more, I'm going to remove these patches for now.