Make this work on FreeBSD.

From my understanding this should make it work on NetBSD and Dragonfly
as well.

Part of #191.

src/portable_endian.h

@@ -55,15 +55,6 @@
 
 #	include <sys/endian.h>
 
-#	define be16toh(x) betoh16(x)
-#	define le16toh(x) letoh16(x)
-
-#	define be32toh(x) betoh32(x)
-#	define le32toh(x) letoh32(x)
-
-#	define be64toh(x) betoh64(x)
-#	define le64toh(x) letoh64(x)
-
 #elif defined(__SunOS)
 
 #	include <sys/types.h>