Revert "Merge: glibc: 2.24 -> 2.25"

This reverts commit 1daf2e26d2, reversing
changes made to c0c50dfcb7.

It seems this is what has been causing all the reliability problems
on Hydra.  I'm currently unable to find why it happens, so I'm forced
to revert the update for now.  Discussion: #22874.

pkgs/development/libraries/fontconfig/default.nix

@@ -28,17 +28,7 @@ stdenv.mkDerivation rec {
       src = ./config-compat.patch;
       inherit configVersion;
     })
-    (fetchpatch {
-      name = "glibc-2.25.diff";
-      url = "https://cgit.freedesktop.org/fontconfig/patch/?id=1ab5258f7c";
-      sha256 = "0x2a4qx51j3gqcp1kp4lisdzmhrkw1zw0r851d82ksgjlc0vkbaz";
-    })
   ];
-  # additionally required for the glibc-2.25 patch; avoid requiring gperf
-  postPatch = ''
-    sed s/CHAR_WIDTH/CHARWIDTH/g -i src/fcobjshash.{h,gperf}
-    touch src/*
-  '';
 
   outputs = [ "bin" "dev" "lib" "out" ]; # $out contains all the config