fontconfig_210: Remove reference to obsolete patch

Commit 9b049849bf deleted the patch file
(and reference to it from fontconfig default.nix), but left the one in
2.10.nix which break evaluation.

As the package seems to build fine without the patch, just remove the
reference.

cc @ttuegel in case this was not the correct thing to do.

pkgs/development/libraries/fontconfig/2.10.nix

@@ -8,12 +8,6 @@ stdenv.mkDerivation rec {
     sha256 = "0llraqw86jmw4vzv7inskp3xxm2gc64my08iwq5mzncgfdbfza4f";
   };
 
-  patches = [
-    # FreeType 2.7 prefixes PCF font family names with the foundry name.
-    # The output of fc-list and fc-query change which breaks the tests.
-    ./test-pcf-family-names-freetype-2.7.patch
-  ];
-
   outputs = [ "bin" "dev" "lib" "out" ]; # $out contains all the config
 
   propagatedBuildInputs = [ freetype ];