cpython: fetch darwin-libutil.patch to nixpkgs

python3 is now required buildInput for glibc>=2.29.
Remove fetchpatch to solve infinite recursion in
glibc bootstrap process.

pkgs/development/interpreters/python/cpython/3.7/darwin-libutil.patch

@@ -0,0 +1,23 @@
+diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
+index c3682b4..16826c6 100644
+--- a/Modules/posixmodule.c
++++ b/Modules/posixmodule.c
+@@ -5880,15 +5880,13 @@ error:
+ #if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX)
+ #ifdef HAVE_PTY_H
+ #include <pty.h>
+-#else
++#endif
+ #ifdef HAVE_LIBUTIL_H
+ #include <libutil.h>
+-#else
++#endif
+ #ifdef HAVE_UTIL_H
+ #include <util.h>
+-#endif /* HAVE_UTIL_H */
+-#endif /* HAVE_LIBUTIL_H */
+-#endif /* HAVE_PTY_H */
++#endif
+ #ifdef HAVE_STROPTS_H
+ #include <stropts.h>
+ #endif