python-cffi: remove patch for clang

Builds fine without it now.

pkgs/development/python-modules/cffi/clang.patch

@@ -1,13 +0,0 @@
-diff --git a/testing/cffi1/test_recompiler.py b/testing/cffi1/test_recompiler.py
-index a3277b0..0d6e2c3 100644
---- a/testing/cffi1/test_recompiler.py
-+++ b/testing/cffi1/test_recompiler.py
-@@ -2270,7 +2270,7 @@ def test_char16_char32_type(no_cpp=False):
-         char32_t foo_4bytes(char32_t);
-     """)
-     lib = verify(ffi, "test_char16_char32_type" + no_cpp * "_nocpp", """
--    #if !defined(__cplusplus) || __cplusplus < 201103L
-+    #if !defined(__cplusplus)
-     typedef uint_least16_t char16_t;
-     typedef uint_least32_t char32_t;
-     #endif

pkgs/development/python-modules/cffi/default.nix

@@ -10,8 +10,6 @@ if isPyPy then null else buildPythonPackage rec {
     sha256 = "df9083a992b17a28cd4251a3f5c879e0198bb26c9e808c4647e0a18739f1d11d";
   };
 
-  patches = stdenv.lib.optional (isPy27 && stdenv.cc.isClang) ./clang.patch;
-
   outputs = [ "out" "dev" ];
 
   propagatedBuildInputs = [ libffi pycparser ];