Fix Darwin builds.

From <http://git.savannah.gnu.org/cgit/cpio.git/commit/?id=3a7a1820d4cecbd77c7b74c785af5942510bf080>.
See also <http://lists.gnu.org/archive/html/bug-cpio/2010-07/msg00001.html>.

diff --git a/src/filetypes.h b/src/filetypes.h
index f80faab..81f0c32 100644
--- a/src/filetypes.h
+++ b/src/filetypes.h
@@ -81,5 +81,3 @@
 #ifndef S_ISLNK
 #define lstat stat
 #endif
-int lstat ();
-int stat ();