remove bogus declaration of malloc from tcp_wrappers

The declaration was already inactive when INET6 was enabled
and it causes a build error in the other case because of
a conflict with the correct definition in stdlib.h.

Discussed with:	dim, ume
MFC after:	2 weeks

contrib/tcp_wrappers/scaffold.c

@@ -28,10 +28,6 @@ static char sccs_id[] = "@(#) scaffold.c 1.6 97/03/21 19:27:24";
 #define	INADDR_NONE	(-1)		/* XXX should be 0xffffffff */
 #endif
 
-#ifndef INET6
-extern char *malloc();
-#endif
-
 /* Application-specific. */
 
 #include "tcpd.h"