net/arpd: loosen deps

[Jérémie Courrèges-Anglas]

I don't think arpd needs python.  Makes it available on vax.

Index: Makefile
===================================================================
RCS file: /cvs/ports/net/arpd/Makefile,v
retrieving revision 1.16
diff -u -p -r1.16 Makefile
--- Makefile    15 Oct 2012 15:18:32 -0000      1.16
+++ Makefile    18 Feb 2013 19:14:16 -0000
@@ -23,6 +23,6 @@ USE_GROFF =           Yes
 
 WRKDIST=               ${WRKDIR}/arpd
 
-LIB_DEPENDS=           net/libdnet
+LIB_DEPENDS=           net/libdnet,-main
 
 .include <bsd.port.mk>