poppler: remove qtcairo patch cruft

pkgs/development/libraries/poppler/default.nix

···
   version = "0.32.0"; # even major numbers are stable
   sha256 = "162vfbvbz0frvqyk00ldsbl49h4bj8i8wn0ngfl30xg1lldy6qs9";
 
-  # This is for Okular (and similar) to support subpixel rendering.
-  # It's kept from upstream because of political reasons.
-  qtcairo_patch = fetchpatch {
-    url = "https://github.com/giddie/poppler-qt4-cairo-backend/compare/"
-      + "fa1d636...b30f96c.diff"; # update to current maint...qt4-lcd
-    sha256 = "0g18y247k2vcz1n56rnfpy226f22v4r9c7pk8cf2h9l12vz2qxkm";
-  };
-
   poppler_drv = nameSuff: merge: stdenv.mkDerivation (stdenv.lib.mergeAttrsByFuncDefaultsClean [
   rec {
     name = "poppler-${nameSuff}-${version}";