Don't need an explicit extern vfprintf.

Index: err.c
--- err.c.orig
+++ err.c
@@ -47,7 +47,6 @@
 
 #ifdef __STDC__
 #include <stdarg.h>
-extern vfprintf (FILE *, const char *, va_list);
 #else /* ! __STDC__ */
 #include <varargs.h>
 extern vfprintf ();